Question 325309
 Martin's average score after 4 tests is 89. 
What score on the 5th test would bring Martin's 
average up to exactly 90?
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After 4 tests Martin has 4*89 = 356 points
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Let the 5th score be "x".
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Solve (356+x)/5 = 90
356+x = 450
x = 94
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Cheers,
Stan H.