Katie must take five exams in a math class. If her scores on the first four exams are 76, 74, 90, and 88, what score must Katie get on the fifth exam for her overall mean to be at least 90?

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Answer 1 · 2017-02-27T17:58:26

$122$

Mean = Sum of the tests divided by the total number of tests

Let $x =$ the 5th test score

Mean $= (76+74+90+88+x)/5 = 90$

Solve by first multiplying both sides of the equation by $5$ :

$= (5(76+74+90+88+x))/5 = 90*5$

$= 76+74+90+88+x = 450$

Solve for $x: x = 450 - 76-74-90-88 = 122$