2018 AMC 12A Problem #1

Algebra Level 2

A large urn contains 100 100 balls, of which 36 % 36 \% are red and the rest are blue. How many of the blue balls must be removed so that the percentage of red balls in the urn will be 72 % 72 \% ? (No red balls are to be removed.)

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64 36 28 32 50

Steven Yuan by Steven Yuan , 20, USA

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2 solutions

Zain Majumder
Feb 11, 2018

0.72 x = 36 ⟹ x = 50 0.72x = 36 \implies x=50 .

There needs to be 50 50 balls in the urn, so 50 \boxed{50} must be removed.

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Vin Benzin
Feb 8, 2018

(64 - x)/(100 - x)×100 = 28

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