QG 11 problems

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QG 11 problems

by samsachd » Thu Aug 06, 2009 8:44 pm
Q: If s and t are +ve intergers such that s/t=64.12.Which of the following could be the remainder when s is divided by t?

A) 2
B) 4
C) 8
D) 20
E) 45


Q: The product of all the Prime numbers less than 20 is closest to which of the following powers of 10?
ANS: 10^7.
My point is that is there any other way to solve this kind of questions rather then calculating the product value first.In case some big number ( like (product of all the Prime numbers less than 100) is there then how to solve the question?
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by aspiregmat » Thu Aug 06, 2009 9:18 pm
Q 1: The equation can be reduced to 12/100 .. i.e 3/25 .. Now since denominator is higher numerator itself will be the remainder. The numerator has to be multiple of 3 so ans = 45 E

Q2: If there is a shortcut would love to know...
One guess : Answer choices may help in this particular case. But for big numbers it will be still cumbersome.

In this case answer has to be 6,7 or 8.. We don't need to do complete calculation approximating it will be pretty close to answer( for big numbers doesn't work)

1,2,3,5,7,11,13,17,19
(2,5) = 10
(3,7) = 20
11 = 10
(13,17) = 200
19 = 20

so ans = 7