Thread: Should be simple...

...but I'm afraid I can't recall how to answer such questions:

'After taking 3 math quizzes Elise has an average of 89. What must she score on the fourth quiz to raise her average to 91?'

Help is very much appreciated.

Let her scores in the first three quizzes be respectively.

Given that

so

Now her average in four quizzes would be



x4 is her scr in the 4th quiz.

since



so

Plug in the value of from above and find x4

Thanks very much!