GRE Percents, Ratios, and Proportions 2

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?

Accepted Answer

15

Answer

Boys = (3/8) × 40 = 15.

Question 2

If a:b = 2:3 and b:c = 4:5, what is a:c?

Accepted Answer

8:15

Answer

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?

Accepted Answer

30

Answer

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)?

Accepted Answer

5:2

Answer

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?

Accepted Answer

4

Answer

Flour's share is 4/(4+1) = 4/5 of the total; 4/5 × 5 = 4 cups.

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