Question 164450
You are given 3 scores and asked to find a fourth that results in an average of 87.

The easiest way to go is :
Let X be the fourth test score

{{{AveragePerTest = (Total Score)/(NumberOfTests)}}}

{{{87 = (87 + 81 + 88 + X)/ 4 }}}
{{{87 * 4 = (256 + X) }}}
{{{348 = 256 + X }}}
{{{348 - 256 = X }}}
{{{92 = X }}}

better get studying to Ace that thing