GRE Percents, Ratios, and Proportions 2 — Questions and Answers
Question 1: If the ratio of boys to girls in a class is 3:5 and there are 40 students total, how many boys are there?
- 8
- 15 (Correct answer)
- 25
- 24
Correct answer: 15
Boys = (3/8) × 40 = 15.
Question 2: If a:b = 2:3 and b:c = 4:5, what is a:c?
- 8:15 (Correct answer)
- 2:5
- 6:15
- 10:12
Correct answer: 8:15
a/c = (a/b) × (b/c) = (2/3) × (4/5) = 8/15, so a:c = 8:15.
Question 3: The ratio of the length to the width of a rectangle is 5:3. If the perimeter is 96, what is the length?
- 12
- 18
- 24
- 30 (Correct answer)
Correct answer: 30
Let length = 5k and width = 3k; perimeter 2(5k + 3k) = 96 gives k = 6, so length = 30.
Question 4: If x:y = 3:7, what is (x + y):(y − x)?
- 1:4
- 5:2 (Correct answer)
- 4:1
- 2:1
Correct answer: 5:2
Let x = 3k, y = 7k; then x + y = 10k and y − x = 4k, giving the ratio 10:4 = 5:2.
Question 5: A recipe calls for flour and sugar in a ratio of 4:1. If you want to use exactly 5 cups in total, how many cups of flour do you need?
- 1
- 2
- 4 (Correct answer)
- 5
Correct answer: 4
Flour's share is 4/(4+1) = 4/5 of the total; 4/5 × 5 = 4 cups.
Question 6: If the ratio of red to green to blue balls is 2:3:5 and there are 30 blue balls, how many total balls are there?
- 45
- 50
- 60 (Correct answer)
- 75
Correct answer: 60
Blue = 5k = 30, so k = 6; total = (2 + 3 + 5)k = 10 × 6 = 60.
Question 7: In a mixture of juice and water, the ratio is 3:2. After 10 liters of water are added, the ratio becomes 3:4. How much juice was in the original mixture?
- 15 liters (Correct answer)
- 10 liters
- 12 liters
- 6 liters
Correct answer: 15 liters
Let juice = 3k, water = 2k; setting up 3k/(2k + 10) = 3/4 gives k = 5, so juice = 15 liters.
GRE Percents, Ratios, and Proportions 2
If the ratio of boys to girls in a class is 3:5 and there are 40 students total, how many boys are there?