PSAT Math Multiple-Choice Question 643: Answer and Explanation

Question: 643

John's performance on his first test was only 60%. His performance increased by 20% on the next test, and it increased an additional 25% on the third test. What did John earn on the third test, to the nearest whole percent?

• A. 72%
• B. 75%
• C. 90%
• D. 105%

Correct Answer: C

Explanation:

(C) If John's performance increased by 20%, then he performed at 120% of his original performance. 120% can be expressed in decimal form as 1.2, and we can find 120% of his original score of 60 by multiplying the two:

1.2(60) = 72

So John got a 72% on his second test. His performance then increased another 25%, so his third test performance was 125%, or 1.25, of test 2. Therefore, John's third score was:

1.25(72) = 90%

The answer is choice (C).

Alternatively, you could have found John's second score by finding 20% of 60 and adding that to 60:

Test 2 = 60 + (0.2)(60) = 60 + 12 = 72

Then you could have found the third score by finding 25% of 72 and adding that to 72:

Test 3 = 72 + (0.25)(72) = 72 + 18 = 90