GMAT OFFICIAL GUIDE PS

Solution:

We can simplify the given expression by multiplying by 180 and we have:

60 + 45 + 36 + 30 = 20r + 15r + 12r + 10r

171 = 57r

r = 3

Alternate Solution:

We should note that each fraction on the left hand side is 3 times the corresponding fraction on the right.

For instance 1/3 is 3 times 1/9, 1/4 is 3 times 1/12, etc.

Thus, r MUST be 3.

Answer: C

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