ACT Practice Math Questions: Percentages

By Lisa Zimmer Hatch, Scott A. Hatch

If you want a high percentage score on the ACT Math exam, then you should know how to solve percentage problems. As you’ll see in the following practice questions, percentages appear in a wide range of problems, from business math to algebra.

Practice questions

  1. Given that 6 percent of (a + b) = 12 percent of b, which of the following must be true?

    A. a < b
    B. a > b
    C. a = b
    D. a + b = 0
    E. a < 0 and b < 0

  2. The cost of a tablet increased 25 percent from 2014 to 2015. In 2016, the cost of the tablet was 1/4 less than its 2014 cost. By what percentage did the cost of the tablet decrease from 2015 to 2016?

    A. 5%
    B. 25%
    C. 40%
    D. 50%
    E. 75%

Answers and explanations

  1. The correct answer is Choice (C).

    An easy way to deal with percentages is to use the number 100. In this case, say that (a + b) = 100. Then 6 percent of 100 = 6. That means that 12 percent of b is 6. Solve for b:
    ACT_0501
    If a + b = 100, then a = 50 and a = b.

  2. The correct answer is Choice (C).
    Give this problem a real value to work with. Say the 2014 price of the tablet is $100. If the price increased 25 percent between 2014 and 2015, its 2015 price is $125. The next year the price was 1/4 less its 2014 price of $100, which means it cost $75 in 2016. To find the percent decrease between 2015 and 2016, subtract the two prices and divide the difference by the 2015 price:
    ACT_0502
    The percent decrease from 2015 to 2016 is 40 percent.