ASVAB Mathematics Knowledge Practice: Percentages

The Mathematics Knowledge subtest on the ASVAB contains many problems that involve working with percentages. Although calculating percentages is pretty straightforward, you will definitely find a scratch paper and pencil useful, as you’ll see in the following practice questions.

Practice questions

1. 250 is 40 percent of what number?

   A. 650 B. 625 C. 6,250 D. 6,500

2. What is 55 percent of 150?

   A. 75 B. 83.5 C. 80 D. 82.5

Answers and explanations

1. The correct answer is Choice (B).

   To determine a whole number when you know a part and a percent, you can use a proportion; let x equal the whole. The proportion looks like this:

   

   Plug in the numbers you know:

   

   Cancel out the zeros in the fraction to make the problem a bit easier:

   

   (Remember, though, you can't cancel out zeros on the other side of the equals sign.) Divide both sides by 4 to isolate x:

   

   You can check your work by putting the variable in the original equation and making sure the fractions are equal:

   

2. The correct answer is Choice (D).

   You can convert 55 percent into a decimal (0.55) and multiply it by 150 to arrive at the answer, which is 82.5, or you can use a proportion where x equals the number you need to find:

   

   Cross-multiply:

   

   Divide each side by 100 to isolate x:

   You can't use a calculator on the ASVAB, so figure out which method of finding percentages is easiest for you before you take the test.