The average of 4 numbers is 25. If 3 of them are 20, 25 and 30, what is the fourth?
A20
B25CORRECT
C30
D35
GMATQuantitative
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Why the answer is B, and why the others tempt you.
Sum = 4 × 25 = 100. Known three = 75. Fourth = 100 − 75 = 25.
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