Question

2) Joe has an average of 78% after 6 tests. What must he make on his 7th

test in order to have an average of 80?

Answer 1

92%

Explanation:

To get an average generally:

`avg = (a_1+a_2+a_3+...)/(n)`

where n is the amount of numbers you are averaging.

We are not given the sum of the scores of Joe's 6 tests, but we can find it by plugging into the formula.

`78 = (x)/(6)`

where x is the sum of his first 6 tests. Solving for x:

`x = 78(6)\\x = 468`

We can use this sum to substitute for the first 6 tests in order to find the score of the 7th test.

`80 = (468+y)/(7)`

where y is the score of the 7th test that will result in an average of 80. We now simply solve for y:

`7(80) = 468 + y\\560-468 = y\\y = 92`

So, Joe must receive a score of 92% on his 7th test in order to have an average of 80%.