SOLUTION: I would like to know how to find the average of 4 numbers when only 3 are given here's the question (I don't want the answer just to know how to do it); A student has earn

Question 608430: I would like to know how to find the average of 4 numbers when only 3 are given
here's the question (I don't want the answer just to know how to do it); A student has earned scores of 87, 81, and 88 on the first 3 of 4 tests. If the student wants an average (arithmetic mean) of exactly 87, what score must she earn on the fourth test?
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
here's the question (I don't want the answer just to know how to do it); A student has earned scores of 87, 81, and 88 on the first 3 of 4 tests. If the student wants an average (arithmetic mean) of exactly 87, what score must she earn on the fourth test?
Let x = score of fourth test
then
(87+81+88+x)/4 = 87
(256+x)/4 = 87
multiplying both sides by 4:
256+x = 348
x = 348-256
x = 92

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