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GMAT factorial question

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Senior | Next Rank: 100 Posts
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GMAT factorial question

by Baldini » Fri Mar 06, 2009 6:24 am
If (1/5)^m x (1/4)^18= 1/(2(10)^35), then m =

a. 17
b. 18
c. 34
d. 35
e. 36

Any ideas anyone?
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by praxis » Fri Mar 06, 2009 6:37 am
(1/5)^m x (1/4)^18= 1/(2*(10)^35)

can be simplified by multiplying through by 4^18 = 2^36 and then collecting terms under common exponents:

(1/5)^m = (2^36) / (2 * 10^35) = 2^35 / 10^35
= (2/10)^35 = (1/5)^36

So m = 36.

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by pakaskwa » Fri Mar 06, 2009 6:46 am
(1/5)^m = (2^36) / (2 * 10^35) = 2^35 / 10^35
= (2/10)^35 = (1/5)^36
The only problem is that (2/10)^35 = (1/5)^35. So m=35.
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by Baldini » Fri Mar 06, 2009 7:38 am
OA is d
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