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gmatprep probability

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by ssmiles08 » Tue Jun 30, 2009 5:51 pm
probability of getting a question right is 1/2.

(1/2)^x <= 1/1000

take reciprocal, 2^x <= 1000

if you know your powers of 2, 2^10 = 1024 which is little more than 1000, so the number of questions would fall below 10.

(B)
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by benissleeping » Wed Jul 01, 2009 5:57 am
Is there any quick way of knowing/calculating 2^10?
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by benissleeping » Wed Jul 01, 2009 6:01 am
Actually nvm

Its just 32*32 which can be done quite quickly on paper
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by ghacker » Thu Jul 02, 2009 8:48 am
Answer is B

We can calculate 2^10 = (32)^2

How to find 32^2

Fist unit digit is 4 (2x2)
Tens digit is ( 3*2*2) = 2 (take one to the Hundred)
Hundred digit = 3*3 +1(0verflow from tens digit) = 10

32^2 = 1024
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