Working with Formulas

Question

In math class, you have the following scores: 77 , 82 , and 73. If the last test has a maximum of 100 points, what score do you need for an average of 80?

Answer 1

Remember that an average is the following:

Adding all of the scores together / The number of Scores

So in this case, we are adding a fourth score, X.

Now we know we have 4 scores, so the denominator will be 4!

We need to find the X so that the new average will be 80.... so we need to find X:

(77 + 73 + 82 + X)/ 4 = 80

(X+232)/4 = 80

X+232 = 320

X = 320 - 232

X = 88

Answer 2

Assuming that each test counts as 1/4 of your grade:

Let x = score on the fourth test

(77 + 82 + 73 + x) / 4 = 80

232 + x = 320

x = 88

You need a score of 88 on the fourth test to have an 80 average.