Silvia's test scores are 86, 78, and 92. What must she score on her fourth test in order to have an average of 85 for all four tests?

A.) 74

B.) 90

C.) 75

D.) 84

The answer is D.

To find this, you need to do (86+78+92+x) / 4=85

You then multiply 4 to each side (to isolate x)

You are left with (86+78+92+x) = 340

You can then subtract 256 (the value of 86+78+92) from both sides.

You then have x=84

Therefore, you know she must score an 84 on her next test to average an 85.

The answer is d. 84

if you add 86, 78, and 92 together you get 256. then when you add 84 to that you get 340. then divide 340 by 4 (you divide by 4 because 4 answers made up the total of 340) to get 85.