What score must tony make on his next quiz in order to keep his Average at 85% his current quiz scores are 90,70,85 and 80

Answer 1

He has 4 test scores, so the next test makes 5. The average will be the sum of the 5 scores divided by 5.

Write the equation:

85 = SUM / 5

So, SUM = 425

Then subtract the total of the 1st 4 tests to get your answer.

For anything like this---CHECK your answer--in this case, calculate the average of the 5 values to be sure you get the right answer.