One- and Two-Step Equations

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ISEE Middle Level: Quantitative Reasoning › One- and Two-Step Equations

Questions 1 - 10
1

A sequence of numbers is generated by the rule \(3n - 5\), where \(n\) is the position of the number in the sequence. Which term in the sequence has a value of 49?

142nd

54th

16th

18th

Explanation

We are looking for the value of \(n\) when the term's value is 49. Set up the equation: \(3n - 5 = 49\). Add 5 to both sides: \(3n = 54\). Divide by 3: \(n = 18\). So, the 18th term in the sequence has a value of 49. Distractor C is the intermediate value of \(3n\). Distractor D is the value of the 49th term (\(3(49) - 5 = 147 - 5 = 142\)). Distractor A is a result of an estimation or calculation error.

2

The perimeter of a rectangle is 54 cm. The length of the rectangle is 3 cm more than twice its width. What is the width of the rectangle in centimeters?

8

17

19

25.5

Explanation

Let \(w\) be the width. The length \(l\) is \(2w + 3\). The formula for the perimeter of a rectangle is \(P = 2(l + w)\). Substitute the given values and expressions: \(54 = 2((2w + 3) + w)\). Simplify the expression inside the parentheses: \(54 = 2(3w + 3)\). Distribute the 2: \(54 = 6w + 6\). Subtract 6 from both sides: \(48 = 6w\). Divide by 6: \(w = 8\). The width is 8 cm. Distractor B (17) comes from using \(l + w = 54\) instead of \(2(l + w) = 54\). Distractor C (19) is the length. Distractor D (25.5) comes from solving \(2w + 3 = 54\) directly.

3

When a number \(k\) is divided by 4 and then 9 is added to the result, the answer is 15. What is the value of \(k - 2\)?

22

24

49

94

Explanation

First, set up the equation to find \(k\): \(\frac{k}{4} + 9 = 15\). Subtract 9 from both sides: \(\frac{k}{4} = 6\). Multiply both sides by 4: \(k = 24\). The question asks for the value of \(k - 2\), not \(k\). So, substitute the value of \(k\): \(24 - 2 = 22\). Distractor B is the value of \(k\). Distractor C results from misinterpreting the order of operations as \(\frac{k+9}{4}=15\), which gives \(k+9=60\) and \(k=51\), so \(k-2=49\). Distractor D results from adding 9 instead of subtracting: \(\frac{k}{4}=15+9=24\), so \(k=96\) and \(k-2=94\).

4

The sum of three consecutive odd integers is 87. What is the largest of these three integers?

27

29

30

31

Explanation

Let the three consecutive odd integers be \(n\), \(n+2\), and \(n+4\). Their sum is \(n + (n+2) + (n+4) = 87\). Combining like terms gives \(3n + 6 = 87\). Subtracting 6 from both sides gives \(3n = 81\). Dividing by 3 gives \(n = 27\). This is the smallest of the three integers. The integers are 27, 29, and 31. The largest is 31. Distractor A is the smallest integer. Distractor B is the middle integer (which is also the average, \(87 \div 3 = 29\)). Distractor C is incorrect because the integer must be odd.

5

The result of dividing a number \(p\) by -6 is 8. What is the result of dividing \(p\) by 4?

-48

-12

5.33

12

Explanation

First, find the value of \(p\). The problem states \(\frac{p}{-6} = 8\). To solve for \(p\), multiply both sides by -6: \(p = 8 \times(-6) = -48\). Next, divide \(p\) by 4: \(\frac{-48}{4} = -12\). The final result is -12. Distractor C is the value of \(p\). Distractor A is the result of a sign error when finding \(p\) (if \(p=48\)) or when performing the final division. Distractor D does not follow from a likely calculation error.

6

A store owner buys a tablet for a certain cost, \(c\). To set the selling price, she marks up the cost by 25%. If the final selling price is $300, what was the original cost, \(c\)?

$225

$240

$275

$375

Explanation

The selling price is the original cost plus a 25% markup. This can be written as \(c + 0.25c = 300\), or \(1.25c = 300\). To find the original cost \(c\), divide the selling price by 1.25: \(c = 300 \div 1.25 = 240\). The original cost was $240. Distractor A is a common error where one finds 25% of the selling price (\(0.25 \times 300 = 75\)) and subtracts it from the selling price (\(300 - 75 = 225\)). Distractor D is another common error where one finds 25% of the cost and adds it to the selling price.

7

The formula to convert temperature from Celsius (C) to Fahrenheit (F) is \(F = \frac{9}{5}C + 32\). If the temperature is 86°F, what is the temperature in degrees Celsius?

30

48

54

97.2

Explanation

Substitute 86 for F in the formula: \(86 = \frac{9}{5}C + 32\). First, subtract 32 from both sides: \(86 - 32 = \frac{9}{5}C\), which simplifies to \(54 = \frac{9}{5}C\). To solve for C, multiply both sides by the reciprocal of \(\frac{9}{5}\), which is \(\frac{5}{9}\): \(C = 54 \times \frac{5}{9}\). This can be calculated as \((54 \div 9) \times 5 = 6 \times 5 = 30\). The temperature is 30°C. Distractor C is the intermediate result before multiplying by the reciprocal. Distractor D is the result of multiplying 54 by \(\frac{9}{5}\) instead of \(\frac{5}{9}\).

8

An isosceles triangle has a perimeter of 39 inches. The base is 6 inches longer than each of the two equal sides. What is the length of the base?

17 inches

21 inches

11 inches

15 inches

Explanation

Let \(s\) be the length of each of the two equal sides. The base \(b\) is \(s + 6\). The perimeter is the sum of the three sides: \(s + s + b = 39\). Substitute the expression for \(b\): \(s + s + (s + 6) = 39\). Combine like terms: \(3s + 6 = 39\). Subtract 6 from both sides: \(3s = 33\). Divide by 3: \(s = 11\). This is the length of an equal side. The question asks for the length of the base, which is \(s + 6 = 11 + 6 = 17\) inches. Distractor A is the length of one of the equal sides. Distractors B and D are calculation errors.

9

A number \(n\) is decreased by 6, and the result is multiplied by -3. The final result is 24.

Column A

\(n\)

Column B

-2

The quantity in Column A is greater.

The quantity in Column B is greater.

The two quantities are equal.

The relationship cannot be determined from the information given.

Explanation

First, set up the equation based on the information given: \(-3(n - 6) = 24\). To solve for \(n\), first divide both sides by -3: \(n - 6 = 24 \div(-3)\), which simplifies to \(n - 6 = -8\). Then, add 6 to both sides: \(n = -8 + 6\), which gives \(n = -2\). Therefore, the value in Column A is -2. The value in Column B is also -2. The two quantities are equal. A common mistake is a sign error in distribution (\(-3n - 18 = 24 \implies -3n = 42 \implies n = -14\), leading to B) or in solving (\(n - 6 = -8 \implies n = -14\), leading to B).

10

A phone company charges $0.20 for the first minute of a call and $0.08 for each additional minute. If a call costs $1.24, what was the total duration of the call in minutes?

12

13

14

15.5

Explanation

Let \(m\) be the total number of minutes. The cost is for the first minute plus the additional minutes. The cost of the additional minutes is \($1.24 - $0.20 = $1.04\). The number of additional minutes is the cost of additional minutes divided by the rate: \($1.04 \div $0.08 = 13\). These are the additional minutes. The total duration is the first minute plus the additional minutes: \(1 + 13 = 14\) minutes. Distractor B is the number of additional minutes, not the total duration. Distractor A is an estimation error. Distractor D is the result of dividing the total cost by the additional minute rate \($1.24 / 0.08 = 15.5\), which ignores the special rate for the first minute.

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