Business Analytics Quiz: Linear Programming
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Linear ProgrammingQuestion 1 of 10

A furniture manufacturer produces desks and chairs. Each desk contributes 7070 dollars and requires 33 carpentry hours and 22 finishing hours. Each chair contributes 110110 dollars and requires 44 carpentry hours and 33 finishing hours. Weekly availability is 240240 carpentry hours and 180180 finishing hours. A contract requires at least 2020 desks, while demand limits chair sales to 4040. Let xx and yy denote the numbers of desks and chairs produced.

Which linear programming formulation correctly represents the manufacturer's weekly production decision?

max70x+110y\max 70x+110y subject to 3x+4y2403x+4y\le240, 2x+3y1802x+3y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0.
max110x+70y\max 110x+70y subject to 3x+4y2403x+4y\le240, 2x+3y1802x+3y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0.
max70x+110y\max 70x+110y subject to 3x+4y2403x+4y\ge240, 2x+3y1802x+3y\ge180, x20x\le20, y40y\ge40, and x,y0x,y\ge0.
max70x+110y\max 70x+110y subject to 4x+3y2404x+3y\le240, 3x+2y1803x+2y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0.
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Business Analytics Quiz

Business Analytics Quiz: Linear Programming

Practice Linear Programming in Business Analytics with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Linear Programming, giving you a quick way to practice the rules, question types, and explanations that matter most for Business Analytics.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A furniture manufacturer produces desks and chairs. Each desk contributes 7070 dollars and requires 33 carpentry hours and 22 finishing hours. Each chair contributes 110110 dollars and requires 44 carpentry hours and 33 finishing hours. Weekly availability is 240240 carpentry hours and 180180 finishing hours. A contract requires at least 2020 desks, while demand limits chair sales to 4040. Let xx and yy denote the numbers of desks and chairs produced.

Which linear programming formulation correctly represents the manufacturer's weekly production decision?

  1. max70x+110y\max 70x+110y subject to 3x+4y2403x+4y\le240, 2x+3y1802x+3y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0. (correct answer)
  2. max110x+70y\max 110x+70y subject to 3x+4y2403x+4y\le240, 2x+3y1802x+3y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0.
  3. max70x+110y\max 70x+110y subject to 3x+4y2403x+4y\ge240, 2x+3y1802x+3y\ge180, x20x\le20, y40y\ge40, and x,y0x,y\ge0.
  4. max70x+110y\max 70x+110y subject to 4x+3y2404x+3y\le240, 3x+2y1803x+2y\le180, x20x\ge20, y40y\le40, and x,y0x,y\ge0.
Explanation: When building a linear programming model, your job is to match each element of the problem narrative to the right mathematical structure: an objective function that captures what you're optimizing, constraints that capture resource limits, and bounds that capture contractual or market requirements. Here, the manufacturer wants to maximize weekly contribution, and the contributions are $70\$70 per desk (xx) and $110\$110 per chair (yy). So the objective must be max 70x+110y\max\ 70x + 110y. The carpentry constraint uses 33 hours per desk and 44 per chair against a 240-hour limit: 3x+4y2403x + 4y \le 240. The finishing constraint uses 22 hours per desk and 33 per chair against 180 hours: 2x+3y1802x + 3y \le 180. The contract floor on desks gives x20x \ge 20, and the demand ceiling on chairs gives y40y \le 40. That's exactly Answer A. Answer B swaps the contribution coefficients, assigning $110\$110 to desks and $70\$70 to chairs — the opposite of what the problem states. This would steer the model toward the wrong product mix. Answer C gets the objective right but flips all the inequality directions: resource constraints become \ge (implying you must exceed capacity, which makes no sense), and the desk/chair bounds are inverted (x20x \le 20 and y40y \ge 40), reversing the contract minimum and demand maximum. Answer D also has the right objective but swaps the carpentry and finishing coefficients between the two constraints, misattributing resource usage and producing a structurally different feasible region. A reliable strategy: read the problem column by column — identify the decision variables, then map each resource row carefully. Swapped coefficients and flipped inequalities are the two most common traps in LP formulation questions.

Question 2

A retailer allocates a promotional budget between digital and traditional media. Let dd and tt be the amounts, in thousands of dollars, allocated to digital and traditional media. Management requires digital media to receive at least 40%40\% of total promotional spending. Total spending cannot exceed 120120 thousand dollars, and at least 3030 thousand dollars must be allocated to traditional media.

Which set of constraints correctly represents all three requirements?

  1. d0.40(d+t)d\ge0.40(d+t), d+t120d+t\le120, t30t\ge30, and d,t0d,t\ge0. (correct answer)
  2. d0.40td\ge0.40t, d+t120d+t\le120, t30t\ge30, and d,t0d,t\ge0.
  3. d0.40(d+t)d\le0.40(d+t), d+t120d+t\le120, t30t\ge30, and d,t0d,t\ge0.
  4. d0.60(d+t)d\ge0.60(d+t), d+t120d+t\le120, t30t\ge30, and d,t0d,t\ge0.
Explanation: When translating word problems into linear constraints, your job is to convert each plain-language requirement into a precise mathematical inequality — paying close attention to what each percentage or threshold is actually relative to. The first requirement says digital spending must be at least 40% of total spending, meaning d0.40(d+t)d \ge 0.40(d+t). Notice the base is the total (d+t)(d+t), not just the other category. The second constraint caps total spending: d+t120d+t \le 120. The third sets a floor on traditional spending: t30t \ge 30. Together with non-negativity, this is exactly what Answer A states — making it correct. Here's why the distractors fail: Answer B writes d0.40td \ge 0.40t, which compares digital spending to traditional spending alone, not to the total budget. This is a classic misreading — "40% of total" is not the same as "40% of the other category." Answer C flips the inequality to d0.40(d+t)d \le 0.40(d+t), which would mean digital receives at most 40% of total spending — the opposite of the requirement. Answer D uses d0.60(d+t)d \ge 0.60(d+t), which would require digital to be at least 60% of total spending. While 60% is the complement of 40% (i.e., the share that could go to traditional), the requirement is specifically about digital's minimum share, which is 40%, not 60%. A useful habit: whenever you see "at least X% of total," immediately write it as amountX%×(sum of all categories)\text{amount} \ge X\% \times (\text{sum of all categories}). This prevents both the complement-confusion trap (D) and the wrong-base trap (B).

Question 3

A service center forecasts 1,8001{,}800 routine tickets requiring 88 minutes each and 600600 complex tickets requiring 1818 minutes each. Existing staff can supply 260260 productive hours during the planning period. Each additional full-time staff equivalent supplies 3232 productive hours and costs 1,2001{,}200 dollars; each part-time staff equivalent supplies 1414 productive hours and costs 600600 dollars. For an initial linear programming plan, fractional staff equivalents are allowed. Let xx and yy be additional full-time and part-time staff equivalents.

Which model component correctly represents the staffing objective and coverage requirement?

  1. min1200x+600y\min 1200x+600y subject to 32x+14y16032x+14y\ge160 and x,y0x,y\ge0. (correct answer)
  2. min1200x+600y\min 1200x+600y subject to 32x+14y42032x+14y\ge420 and x,y0x,y\ge0.
  3. min1200x+600y\min 1200x+600y subject to 32x+14y26032x+14y\ge260 and x,y0x,y\ge0.
  4. min1200x+600y\min 1200x+600y subject to 32x+14y16032x+14y\le160 and x,y0x,y\ge0.
Explanation: When tackling workforce planning LP problems, your first move should always be to convert demand into the unit your constraint is measured in — here, productive hours — then compare that total against existing supply to find the gap that additional staff must cover. Start with total hours required: 1,800×860+600×1860=240+180=4201{,}800 \times \frac{8}{60} + 600 \times \frac{18}{60} = 240 + 180 = 420 hours demanded. Existing staff already supplies 260260 hours, leaving a shortfall of 420260=160420 - 260 = 160 hours. The objective is to minimize the cost of covering that gap: min1200x+600y\min 1200x + 600y, subject to additional staff providing at least 160160 hours — giving 32x+14y16032x + 14y \ge 160. That's exactly answer A, which is correct. Answer B uses 32x+14y42032x + 14y \ge 420, which ignores existing staff entirely and treats the full demand as if zero coverage already exists — a classic trap when you forget to subtract current capacity from total need. Answer C uses 32x+14y26032x + 14y \ge 260, which confuses existing staff supply (260260 hours) for the required additional hours — essentially setting the constraint equal to what you already have rather than what you still need. Answer D flips the inequality to 160\le 160, which would limit additional hours rather than guarantee a minimum — this would minimize cost by hiring nobody, completely defeating the purpose of a coverage constraint. As a strategy tip: in any resource-gap LP, always compute (total demand) − (existing supply) = required addition, and remember that coverage constraints use \ge (you must meet or exceed the gap, not cap it).

Question 4

An analyst is optimizing advertising allocations using predicted lead rates. For each thousand impressions, channel A generates 2424 leads with a contribution of 5050 dollars per lead and costs 400400 dollars. Channel B generates 1818 leads with a contribution of 7070 dollars per lead and costs 350350 dollars. Let xx and yy be thousands of impressions purchased from channels A and B. The media budget is 35,00035{,}000 dollars.

Which formulation correctly maximizes predicted net contribution while enforcing the media budget?

  1. max800x+1260y\max 800x+1260y subject to 400x+350y35000400x+350y\le35000 and x,y0x,y\ge0.
  2. max1200x+1260y\max 1200x+1260y subject to 400x+350y35000400x+350y\le35000 and x,y0x,y\ge0.
  3. max800x+910y\max 800x+910y subject to 400x+350y35000400x+350y\le35000 and x,y0x,y\ge0. (correct answer)
  4. max0.80x+0.91y\max 0.80x+0.91y subject to 400x+350y35000400x+350y\le35000 and x,y0x,y\ge0.
Explanation: When building a linear programming model for net contribution, you need to carefully distinguish between gross revenue and net contribution — that is, revenue minus cost. For each unit of decision variable (thousands of impressions), the objective coefficient must capture what's left after paying for that channel. For Channel A, one thousand impressions generates 2424 leads at $50\$50 each, producing 24×50=$1,20024 \times 50 = \$1{,}200 in gross contribution. Subtract the $400\$400 cost, and the net contribution per thousand impressions is $800\$800. For Channel B, 18×70=$1,26018 \times 70 = \$1{,}260 gross, minus $350\$350 cost, yields $910\$910 net. So the correct objective is max 800x+910y\max\ 800x + 910y, subject to the budget constraint 400x+350y35,000400x + 350y \le 35{,}000, confirming C. Choice A uses 800x800x correctly for Channel A but mistakenly uses 1,260y1{,}260y for Channel B — that's the gross contribution, ignoring the $350\$350 cost. Choice B compounds the error by using gross values for both channels: 1,200x+1,260y1{,}200x + 1{,}260y omits all media costs from the objective entirely. Choice D appears to compute some ratio (roughly gross/cost), but 0.800.80 and 0.910.91 have no coherent interpretation as contribution dollars — they're dimensionally wrong and would give a meaningless optimization. A reliable strategy: always build objective coefficients by asking "if I buy one unit of this variable, what do I earn minus what do I spend?" Confusing gross revenue with net contribution is the most common trap in media-mix optimization problems, so make that subtraction explicit before writing your objective function.

Question 5

A manufacturer produces products xx and yy. The proposed linear program includes the constraints 3x+2y1203x+2y\le120 for material, x+4y100x+4y\le100 for labor, x20x\ge20 and y10y\ge10 for customer commitments, and x+y45x+y\ge45 for total contracted output.

Which proposed production plan is feasible?

  1. Produce 2828 units of xx and 1717 units of yy. (correct answer)
  2. Produce 3131 units of xx and 1414 units of yy.
  3. Produce 2626 units of xx and 1919 units of yy.
  4. Produce 3232 units of xx and 1212 units of yy.
Explanation: When checking feasibility in a linear program, your job is simple: plug each proposed solution into every constraint and confirm all of them are satisfied simultaneously. One violation disqualifies the entire plan. The five constraints here are: 3x+2y1203x+2y\le120, x+4y100x+4y\le100, x20x\ge20, y10y\ge10, and x+y45x+y\ge45. Option A (x=28,y=17x=28, y=17) passes every check: 3(28)+2(17)=1181203(28)+2(17)=118\le120 ✓, 28+4(17)=9610028+4(17)=96\le100 ✓, 282028\ge20 ✓, 171017\ge10 ✓, and 28+17=454528+17=45\ge45 ✓. This is your feasible plan. Option B (x=31,y=14x=31, y=14) fails the labor constraint: 31+4(14)=8710031+4(14)=87\le100 ✓, but 3(31)+2(14)=121>1203(31)+2(14)=121>120 — the material constraint is violated by 1 unit. Option C (x=26,y=19x=26, y=19) fails the minimum output commitment: x20x\ge20 ✓ and y10y\ge10 ✓, but 26+19=454526+19=45\ge45 ✓ — actually check material: 3(26)+2(19)=1161203(26)+2(19)=116\le120 ✓, labor: 26+4(19)=102>10026+4(19)=102>100 ✗. Labor is violated. Option D (x=32,y=12x=32, y=12) also fails labor: 32+4(12)=8010032+4(12)=80\le100 ✓, but 3(32)+2(12)=1201203(32)+2(12)=120\le120 ✓, 32+12=44<4532+12=44<45 ✗. The total contracted output minimum is not met. A practical strategy: always test the tightest or most easily overlooked constraints first — minimums like x+y45x+y\ge45 are traps students frequently skip because they focus on the "less than" resource constraints.

Question 6

A distributor begins the month with 8080 units of inventory and must satisfy demand for 500500 units during the month. Let xx be units purchased during the month and ee be ending inventory. All demand must be met, and no lost sales or disposal are allowed.

Which linear constraint correctly represents inventory flow?

  1. 80+e=500+x80+e=500+x, with x,e0x,e\ge0.
  2. 80+x+e=50080+x+e=500, with x,e0x,e\ge0.
  3. x=80+500+ex=80+500+e, with x,e0x,e\ge0.
  4. 80+x=500+e80+x=500+e, with x,e0x,e\ge0. (correct answer)
Explanation: Whenever you see an inventory or material-flow problem, your instinct should be to write a simple conservation equation: what you start with, plus what comes in, must equal what goes out, plus what remains. Think of it like a bathtub — beginning water plus water added equals water drained plus water left. Here, the distributor begins with 8080 units and purchases xx units, so total supply available is 80+x80 + x. That supply is used to satisfy demand of 500500 units, with ee units left over as ending inventory. Setting supply equal to demand plus leftovers gives you 80+x=500+e80 + x = 500 + e, with x,e0x, e \ge 0 — which is exactly answer D. You can verify the logic by rearranging: x=420+ex = 420 + e, meaning at minimum (when e=0e = 0) you must purchase 420420 units to cover the 420420-unit shortfall between beginning inventory and demand. A rearranges to 80+ex=50080 + e - x = 500, which incorrectly subtracts purchases instead of adding them — treating buying as a reduction in supply rather than an addition. B writes 80+x+e=50080 + x + e = 500, which says the ending inventory comes out of available supply without accounting for demand being a separate outflow — it conflates demand with the total rather than treating it as a use of inventory. C writes x=80+500+ex = 80 + 500 + e, dramatically overstating purchases by adding beginning inventory and demand together as if both were costs to buy against. A reliable study tip: always label your flows explicitly — in (beginning inventory + purchases) and out (demand + ending inventory) — then set them equal. This structure prevents every mistake shown in A, B, and C.

Question 7

A manufacturer can purchase overtime labor in two ordered tiers. The first 100100 overtime hours cost 3030 dollars per hour, and any additional overtime hours cost 4545 dollars per hour. Let o1o_1 and o2o_2 represent hours purchased in the first and second tiers, and let HH be the overtime hours required by the production plan. The overall model minimizes cost.

Which linear formulation correctly represents overtime coverage and tiered cost?

  1. min30o1+45o2\min 30o_1+45o_2 subject to o1+o2Ho_1+o_2\ge H, o10o_1\ge0, and 0o21000\le o_2\le100.
  2. min30o1+45o2\min 30o_1+45o_2 subject to o1+o2Ho_1+o_2\ge H, 0o11000\le o_1\le100, and o20o_2\ge0. (correct answer)
  3. min45o1+30o2\min 45o_1+30o_2 subject to o1+o2Ho_1+o_2\ge H, 0o11000\le o_1\le100, and o20o_2\ge0.
  4. min30o1+30o2\min 30o_1+30o_2 subject to o1+o2Ho_1+o_2\ge H, 0o11000\le o_1\le100, and o20o_2\ge0.
Explanation: When modeling tiered pricing in linear programming, your goal is to capture two things: (1) the correct cost structure for each tier, and (2) the capacity constraint that forces cheaper hours to be used first before spilling into the more expensive tier. Here, the first 100100 hours cost $30\$30 each (tier 1, variable o1o_1), and any hours beyond that cost $45\$45 each (tier 2, variable o2o_2). Because the model minimizes cost, a cost-minimizing solver will naturally exhaust the cheaper tier before using the expensive one — but only if o1o_1 is capped at 100100. That cap is the key structural requirement. Answer B gets this exactly right: the objective min30o1+45o2\min 30o_1 + 45o_2 correctly assigns the lower rate to tier 1 and higher rate to tier 2. The coverage constraint o1+o2Ho_1 + o_2 \ge H ensures total hours meet demand. The bounds 0o11000 \le o_1 \le 100 and o20o_2 \ge 0 enforce the tier-1 cap while allowing unlimited tier-2 hours. Answer A swaps the caps — it limits o2100o_2 \le 100 instead of o1o_1, which incorrectly restricts the expensive tier rather than the cheap one, leaving the cheaper tier unbounded. Answer C reverses the costs in the objective (45o1+30o245o_1 + 30o_2), effectively labeling the cheaper tier as expensive and vice versa — a straightforward mix-up of the rate assignments. Answer D assigns $30\$30 to both tiers, ignoring the second-tier premium entirely and understating costs. A useful rule of thumb: in any tiered-cost LP, the cheaper tier gets the binding upper bound, while the pricier tier stays uncapped. The minimizing objective does the rest automatically.

Question 8

A subscription company offers standard and premium packages. Let ss and pp denote the numbers of standard and premium packages sold. To limit support demand, the company may sell at most 33 premium packages for every 55 standard packages. It must sell at least 120120 packages in total and at least 2020 premium packages.

Which set of constraints correctly represents these requirements?

  1. 3p5s3p\le5s, s+p120s+p\ge120, p20p\ge20, and s,p0s,p\ge0.
  2. 5p3s5p\le3s, s+p120s+p\ge120, p20p\ge20, and s,p0s,p\ge0. (correct answer)
  3. 5p3s5p\ge3s, s+p120s+p\ge120, p20p\ge20, and s,p0s,p\ge0.
  4. 5p3s5p\le3s, s+p120s+p\le120, p20p\ge20, and s,p0s,p\ge0.
Explanation: When translating word problems into linear constraints, your job is to convert each business rule into a precise mathematical inequality — paying close attention to the direction of the inequality and which variable appears on which side. The trickiest constraint here is the ratio rule: "at most 3 premium packages for every 5 standard packages." This means the ratio p/s3/5p/s \le 3/5, or equivalently, multiplying both sides by 5s5s: 5p3s5p \le 3s. Read it plainly — premium is capped relative to standard, so premium gets the larger coefficient on the constrained (left) side. The remaining rules are more direct: total packages must be at least 120, giving s+p120s + p \ge 120, and premium sales must be at least 20, giving p20p \ge 20. Combined with non-negativity, this is exactly what B states, making it the correct answer. Answer A flips the ratio constraint to 3p5s3p \le 5s, which simplifies to p53sp \le \frac{5}{3}s — a much looser restriction that allows far more premium packages than intended. It misrepresents the 3-to-5 ratio entirely. Answer C reverses the inequality to 5p3s5p \ge 3s, which actually requires a high share of premium packages rather than limiting it — the opposite of the business rule. Answer D gets the ratio right (5p3s5p \le 3s) but changes the total packages constraint to s+p120s + p \le 120, turning "at least 120" into "at most 120" — a critical sign error. When you see ratio constraints, always set up the fraction first (p/s3/5p/s \le 3/5), then cross-multiply carefully. Inequality direction errors are the most common trap on these questions.

Question 9

A company is selecting the footprint of a new distribution center. Because of zoning categories, the facility must be either no larger than 4040 thousand square feet or at least 7070 thousand square feet. Let xx denote the footprint in thousands of square feet.

Which statement best describes the condition x40x\le40 or x70x\ge70 in a linear optimization model?

  1. It is equivalent to imposing both x40x\le40 and x70x\ge70 in one continuous linear program.
  2. It is equivalent to the pair of constraints x40x\ge40 and x70x\le70 in one continuous linear program.
  3. It is a disjunctive condition that generally requires a binary variable or two separately solved linear programs. (correct answer)
  4. It is an ordinary continuous linear constraint because each side of the word "or" is individually linear.
Explanation: When you encounter an "or" condition in optimization — especially one where a variable must satisfy one range or another — you're entering the territory of disjunctive constraints. The key question to ask is: can a single, continuous linear program capture this "either/or" logic? The answer is almost never yes. Here, x40x \le 40 or x70x \ge 70 means the feasible region is split into two disconnected intervals: [0,40][0, 40] and [70,)[70, \infty). A standard linear program requires a convex feasible region — one continuous, unbroken set. Two disconnected intervals violate this requirement. To handle the condition properly, you typically introduce a binary variable y{0,1}y \in \{0, 1\} and reformulate: if y=0y = 0, enforce x40x \le 40; if y=1y = 1, enforce x70x \ge 70. Alternatively, you solve two separate LPs — one for each case — and compare. Either way, choice C correctly identifies this as a disjunctive condition requiring special treatment. Choice A is wrong because combining x40x \le 40 and x70x \ge 70 simultaneously in one LP would require xx to be both at most 40 and at least 70 at the same time — an impossible, infeasible contradiction. Choice B flips the inequalities entirely, describing 40x7040 \le x \le 70, which is actually the excluded middle range — the opposite of the intended condition. Choice D is a tempting trap. Yes, each individual constraint is linear, but "or" between two linear constraints creates a non-convex feasible region, which breaks standard LP assumptions. Study tip: Anytime you see "or" connecting two inequality constraints in optimization, flag it immediately as disjunctive — it almost always signals the need for binary (integer) variables or scenario-based LP comparisons.

Question 10

A beverage company must purchase exactly 1,0001{,}000 liters of concentrate from two suppliers. Supplier A's concentrate has a quality score of 92%92\%, and supplier B's concentrate has a quality score of 78%78\%. The combined purchase must have an average quality score of at least 86%86\%. Let aa and bb be liters purchased from suppliers A and B.

Which constraints correctly impose the required quantity and average quality?

  1. a+b1000a+b\le1000 and 0.92a+0.78b0.86(1000)0.92a+0.78b\ge0.86(1000), with a,b0a,b\ge0.
  2. a+b=1000a+b=1000 and 0.92a+0.78b0.86(ab)0.92a+0.78b\ge0.86(a-b), with a,b0a,b\ge0.
  3. a+b=1000a+b=1000 and 0.92a+0.78b0.86(1000)0.92a+0.78b\le0.86(1000), with a,b0a,b\ge0.
  4. a+b=1000a+b=1000 and 0.92a+0.78b0.86(1000)0.92a+0.78b\ge0.86(1000), with a,b0a,b\ge0. (correct answer)
Explanation: When translating a word problem into linear constraints, your job is to convert every "must" or "at least" statement into precise mathematical language — one constraint per condition. Here, two conditions exist: a fixed total quantity and a minimum quality threshold. The total purchase must be exactly 1,000 liters, which means a+b=1000a + b = 1000 (an equality, not an inequality). For the quality constraint, think of it as a weighted average: each liter from Supplier A contributes 0.92 quality units, and each liter from Supplier B contributes 0.78 quality units. The total quality points collected must meet or exceed what 1,000 liters at 86% would produce, giving 0.92a+0.78b0.86(1000)0.92a + 0.78b \ge 0.86(1000). Combined with non-negativity, answer D captures both conditions correctly. Answer A fails on the quantity constraint — using a+b1000a + b \le 1000 allows purchasing fewer than 1,000 liters, which violates the "exactly 1,000" requirement. Answer B uses the correct equality for quantity, but the right-hand side of the quality constraint is 0.86(ab)0.86(a - b), which is meaningless here — the target quality should be applied to the total volume, not the difference between suppliers. Answer C gets the quantity right but flips the inequality on quality: 0.86(1000)\le 0.86(1000) would enforce a maximum quality score, the opposite of what the problem requires. Study tip: Always map each word carefully — "exactly" means ==, "at least" means \ge, and "at most" means \le. When you see weighted average constraints, ask yourself: quality points earned ≥ quality points required at the threshold.