Zach took four biology tests and got scores of 83, 86, 91, and 77. He needs to complete one more test. If he wants to get an average of 85 on all fve tests, what score does he need on his last test?

He needs a score of 88 on his last test.

Step-by-step explanation:

His mean score is the sum of all his scores dvided by the number of tests. Mathematically, that is:

Zach took four biology tests and got scores of 83, 86, 91, and 77. He needs to complete one more test.

In total there are 5 tests, so

His scores are 83, 86, 91, 77 and x. In which x is his score on the last test. So

If he wants to get an average of 85 on all fve tests, what score does he need on his last test?

This is X when M = 85. So

He needs a score of 88 on his last test.