Question

Lucy wants to be exempt from her semester exam. In order for that to happen, she has to average an 85 over 3 test grades. Her first 2 test grades were 81 and 86. What does Lucy need to make on her third test in order to have an exact average of 85 and be exempt from her exam?

Answer 1

Grades to be scored in 3rd exam = 88

Explanation:

Given that average of 3 numbers is 85.

First two numbers are 81 and 86.

To find:

3rd number so that average is 85

Solution:

Let the third number =
`x`

Formula for average is:

`Average = (Sum\ of\ numbers)/(Total\ count\ of\ numbers)`

Here, sum of numbers =
`81+86+x =167+x`

Total count of numbers = 3

`85 = (167+x)/(3)\\\Rightarrow x=255-167\\\Rightarrow \bold{x=88}`

Grades to be scored in 3rd exam = 88