Henrietta hired a tutor to help her improve her math scores. While working with the tutor, she took

Henrietta hired a tutor to help her improve her math scores. While working with the tutor, she took four tests. She scored 10 points better on the second test than she did on the first, 20 points better on the third test than on the first, and 30 points better on the fourth test than on the first. If the mean of these four tests was 70, what was her score on the third test?

Givens:

• Let the first test score be s:
• The second test score is: s + 10
• The third test score is: s + 20
• The fourth test score is: s + 30

The mean of the four tests is 70, found below:
Sum of test scores / Number of Tests = Mean

Plugging in our number, we get:
(s + s + 10 + s + 20 + s + 30) / 4 = 70

Cross multiply and simplify:
4s + 60 = 70 * 4
4s + 60 = 280

To solve this equation for s, we type it in our search engine and we get:
s = 55

So the third test score:
s + 20 = 55 + 20
75