Solve and Graph Linear Inequalities

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7th Grade Math › Solve and Graph Linear Inequalities

Questions 1 - 9
1

Verify whether $x=-2$ is a solution to the inequality $3x-5<4$.

Yes, because $3(-2)-5=-11$ and $-11<4$.

No, because $3(-2)-5=11$ and $11<4$ is false.

No, because $3(-2)-5=-11$ and $-11>4$.

Yes, because $3(-2)-5=1$ and $1<4$.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context, here verifying a value. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left. To verify x=-2 in 3x-5<4, substitute: 3(-2)-5=-6-5=-11, and -11<4 is true, so yes it satisfies. The correct choice A shows this calculation and confirmation. Errors include wrong computation like to 1<4 still yes but incorrect (choice B), claiming -11>4 (choice C), or to 11<4 false (choice D). Steps are substituting the value, simplifying left side, comparing to right with <, and concluding based on truth. Mistakes involve arithmetic errors like sign mishandling or adding instead of subtracting, or reversing the inequality check.

2

To pass a class, your score must be more than 75 points. You have 68 points now. Each completed practice quiz adds 2 points. Let $q$ be the number of quizzes.

Solve the inequality and state the smallest whole number of quizzes you must complete.

Inequality: $68 + 2q > 75$

$q\ge3.5$, so you need at least $3.5$ quizzes.

$q\ge4$, so you need exactly $4$ quizzes.

$q>3.5$, so you need at least $3$ quizzes.

$q>3.5$, so you need at least $4$ quizzes.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context with whole numbers. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this quiz problem needing more than 75 points from 68 plus 2 per quiz, set up 68+2q>75, solve by subtracting 68 (2q>7), dividing by 2 (q>3.5 since 2>0, no flip), and interpret smallest whole number as 4 quizzes since q must be integer. The correct choice A shows q>3.5 and at least 4 quizzes. Errors include using ≥ instead of > (choice C with q≥3.5), rounding down incorrectly (choice B with at least 3), or misstating as exactly 4 (choice D). Steps include: (1) translate 'more than 75' to >75, (2) solve with inverse operations, (3) for strict >, use open circle if graphing, (4) interpret with ceiling to next integer for 'at least'. Context requires whole quizzes, and mistakes involve boundary type or forgetting to round up for strict inequality.

3

A phone plan starts with $50 credit, and you are charged $2.50 per day you use data. You want your remaining credit to be at least $20. Let $d$ be the number of days you use data.

Set up and solve the inequality: $50 - 2.5d \ge 20$

$d\le12$. Interpretation: you can use data for 12 days or fewer.

$d\ge30$. Interpretation: you must use data for at least 30 days.

$d\ge12$. Interpretation: you must use data for at least 12 days.

$d\le30$. Interpretation: you can use data for 30 days or fewer.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this phone plan starting at $50 credit minus $2.50 per data day, at least $20 remaining, set up 50-2.5d≥20, solve by subtracting 50 (-2.5d≥-30), dividing by -2.5 (d≤12, flip since negative), and interpret as 12 or fewer days. The correct choice A shows d≤12 and interpretation of 12 days or fewer. Errors include no flip (choice B with d≥12), wrong constants (choices C and D with d≤30 or d≥30). Steps include: (1) translate 'at least $20' to ≥20, (2) solve by subtracting and dividing with flip for negative, (3) graph would be closed dot at 12 shaded left, (4) interpret as d≤12. Mistakes often involve forgetting to flip when dividing by negative or direction errors.

4

To pass a class, your score must be more than 75 points. You have 68 points now. Each completed practice quiz adds 2 points. Let $q$ be the number of quizzes.

Solve the inequality and state the smallest whole number of quizzes you must complete.

Inequality: $68 + 2q > 75$​​

$q\ge3.5$, so you need at least $3.5$ quizzes.

$q\ge4$, so you need exactly $4$ quizzes.

$q>3.5$, so you need at least $3$ quizzes.

$q>3.5$, so you need at least $4$ quizzes.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context with whole numbers. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this quiz problem needing more than 75 points from 68 plus 2 per quiz, set up 68+2q>75, solve by subtracting 68 (2q>7), dividing by 2 (q>3.5 since 2>0, no flip), and interpret smallest whole number as 4 quizzes since q must be integer. The correct choice A shows q>3.5 and at least 4 quizzes. Errors include using ≥ instead of > (choice C with q≥3.5), rounding down incorrectly (choice B with at least 3), or misstating as exactly 4 (choice D). Steps include: (1) translate 'more than 75' to >75, (2) solve with inverse operations, (3) for strict >, use open circle if graphing, (4) interpret with ceiling to next integer for 'at least'. Context requires whole quizzes, and mistakes involve boundary type or forgetting to round up for strict inequality.

5

A phone plan starts with $50 credit, and you are charged $2.50 per day you use data. You want your remaining credit to be at least $20. Let $d$ be the number of days you use data.

Set up and solve the inequality: $50 - 2.5d \ge 20$​​

$d\ge30$. Interpretation: you must use data for at least 30 days.

$d\ge12$. Interpretation: you must use data for at least 12 days.

$d\le30$. Interpretation: you can use data for 30 days or fewer.

$d\le12$. Interpretation: you can use data for 12 days or fewer.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this phone plan starting at $50 credit minus $2.50 per data day, at least $20 remaining, set up 50-2.5d≥20, solve by subtracting 50 (-2.5d≥-30), dividing by -2.5 (d≤12, flip since negative), and interpret as 12 or fewer days. The correct choice A shows d≤12 and interpretation of 12 days or fewer. Errors include no flip (choice B with d≥12), wrong constants (choices C and D with d≤30 or d≥30). Steps include: (1) translate 'at least $20' to ≥20, (2) solve by subtracting and dividing with flip for negative, (3) graph would be closed dot at 12 shaded left, (4) interpret as d≤12. Mistakes often involve forgetting to flip when dividing by negative or direction errors.

6

What does the solution $v \le 18$ mean in this context: A gym charges $$\10$$ per month plus $$\5$$ per visit, and you want to spend at most $$\100$$ in a month. ($v$ is the number of visits.)

You must visit the gym 18 or more times to stay within the budget.

You can visit the gym 18 or fewer times and still stay within the budget.

You must visit the gym exactly 18 times.

You can visit the gym fewer than 18 times, but not 18 times.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context. Solving is similar to equations but preserves inequality direction—for $px + q \le r$: subtract q ($px \le r - q$), divide by p ($x \le(r - q)/p$ if p>0, flip to $x \ge \ldots$ if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: $5v + 10 \le 100$$5v \le 90$$v \le 18$ graphs as closed dot at 18, shaded left. In this gym context with $10 plus $5 per visit and at most $100, $v \le 18$ means you can visit 18 or fewer times to stay within budget, including 18 exactly. The correct choice B interprets this accurately. Errors include thinking exactly 18 (choice A), reversing to 18 or more (choice C), or excluding 18 (choice D). Steps include solving to $v \le 18$ as in the example, then interpreting in context (18 or less visits, realistic non-negative integers 0 to 18). Mistakes often are misinterpreting ≤ as > or excluding the boundary, ignoring context like positive visits.

7

A student has 68 points in a class. Each practice quiz adds 2 points. The student needs more than 75 points to earn a B. Let $q$ be the number of quizzes. Solve the inequality and choose the correct statement about how many whole quizzes are needed.

$68+2q>75\Rightarrow 2q>7\Rightarrow q>3.5$, so $q\ge 4$ whole quizzes

$68+2q>75\Rightarrow q>3.5$, so $q=3.5$ quizzes is enough

$68+2q\ge 75\Rightarrow 2q\ge 7\Rightarrow q\ge 3.5$, so $q\ge 3$ whole quizzes

$68+2q>75\Rightarrow 2q>7\Rightarrow q>7$, so $q\ge 8$ whole quizzes

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context, especially with whole numbers. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left. For needing more than 75 points with 68 current and +2 per quiz, set up 68+2q>75, solve by subtracting 68 (2q>7), dividing by 2 (q>3.5), and since quizzes are whole, q≥4 as q=4 gives 76>75 but q=3 gives 74≤75. The correct choice A reflects this with q>3.5 so q≥4 whole quizzes. Errors include using ≥75 leading to q≥3 incorrectly (choice B), dividing wrong to q>7 (choice C), or ignoring whole numbers by suggesting q=3.5 (choice D). Steps are translating 'more than' to >75, solving with inverse operations keeping direction, interpreting for whole q≥4 since context requires integers (can't do half quizzes, round up). Mistakes involve direction errors like using ≥ instead of >, forgetting to round up for strict inequality, or calculation slips like dividing 7 by 2 incorrectly.

8

A student has $x$ minutes of free time. They spend 15 minutes on homework and then want to have at least 25 minutes left to play outside.

Which inequality correctly represents this situation, and what is the solution?

(Assume $x$ is the total free time in minutes.)

Inequality: $x-15\le25$. Solution: $x\le40$. Graph: closed dot at 40, shade left.

Inequality: $15-x\ge25$. Solution: $x\le-10$. Graph: closed dot at -10, shade left.

Inequality: $x+15\ge25$. Solution: $x\ge10$. Graph: closed dot at 10, shade right.

Inequality: $x-15\ge25$. Solution: $x\ge40$. Graph: closed dot at 40, shade right.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this free time problem with x minutes, minus 15 for homework, at least 25 left, the correct inequality is x-15≥25, solving to x≥40, graphed closed dot at 40 shaded right. The correct choice A shows x-15≥25, x≥40, closed dot at 40 shaded right. Errors include wrong direction (choice B with ≤40 shaded left), reversed subtraction (choice C with 15-x≥25 to x≤-10), or addition (choice D with x+15≥25 to x≥10). Steps include: (1) translate 'at least 25 left' to remaining ≥25, so x-15≥25, (2) solve adding 15, no flip, (3) graph closed right for ≥, (4) interpret as x≥40. Common mistakes are inequality setup direction or confusing subtraction with addition.

9

A student has $x$ minutes of free time. They spend 15 minutes on homework and then want to have at least 25 minutes left to play outside.

Which inequality correctly represents this situation, and what is the solution?

(Assume $x$ is the total free time in minutes.)​​

Inequality: $15-x\ge25$. Solution: $x\le-10$. Graph: closed dot at -10, shade left.

Inequality: $x+15\ge25$. Solution: $x\ge10$. Graph: closed dot at 10, shade right.

Inequality: $x-15\le25$. Solution: $x\le40$. Graph: closed dot at 40, shade left.

Inequality: $x-15\ge25$. Solution: $x\ge40$. Graph: closed dot at 40, shade right.

Explanation

This question tests solving two-step linear inequalities from word problems, graphing solution sets on number lines (open/closed dots, directional shading), and interpreting in context. Solving is similar to equations but preserves inequality direction—for px+q≤r: subtract q (px≤r-q), divide by p (x≤(r-q)/p if p>0, flip to x≥... if p<0); graphing uses closed dot ● for ≤ or ≥ (includes boundary), open ○ for < or > (excludes), shade left for < or ≤ (toward smaller), right for > or ≥ (toward larger); example: 5v+10≤100 → 5v≤90 → v≤18 graphs as closed dot at 18, shaded left for 18 or less. For this free time problem with x minutes, minus 15 for homework, at least 25 left, the correct inequality is x-15≥25, solving to x≥40, graphed closed dot at 40 shaded right. The correct choice A shows x-15≥25, x≥40, closed dot at 40 shaded right. Errors include wrong direction (choice B with ≤40 shaded left), reversed subtraction (choice C with 15-x≥25 to x≤-10), or addition (choice D with x+15≥25 to x≥10). Steps include: (1) translate 'at least 25 left' to remaining ≥25, so x-15≥25, (2) solve adding 15, no flip, (3) graph closed right for ≥, (4) interpret as x≥40. Common mistakes are inequality setup direction or confusing subtraction with addition.