Thursday, August 12, 2010

CP #15

From GMATClub Math Book Remainders:

If s and t are positive integer 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


Using the concept,
If you take the decimal portion of the resulting number when you divide by "n", and multiply it to "n", you will get the remainder.
Eg. 8/5 = 1.6
0.6*5 = 3 = remainder

In our question,
0.12*t = R(remainder)
Since R has to be an integer, it must be a multiple of 0.12.
To make the calculation simpler, we multiply both sides by 100.
12*t = 100R

Now, put the value of different Rs in the equation and find which one is perfectly divisible by 12.

i.e. which one of
(A) 200
(B) 400
(C) 800
(D) 2000
(E) 4500
is perfectly divisible by 12 or 3*4.
All are divisible by 4, since they end in 00s.
Only (E) is divisible by 3 also (4+5=9).

Answer is therefore, (E) 45.

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