Operatons on rational numbers

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Operatons on rational numbers

by carllecat » Fri Feb 27, 2009 7:38 am
I took this one from theQuant Sample Questions in the Diagnostic Test of OG11 (Question 13). The given explanation is not crystal clear and I am pretty sure some of you can give a better explanation.

If s and t are positive integers 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

The explanation:
The given equation can be written as 64.12t = s. By splitting portions of t into its integer multiple and its decimal multiple, this become 64t + 0.12 t = s, or 0.12t = s - 64t, which is the remainder. So, 0.12t = remainder. Test the answer choices to find the situation in which t is an integer.

A 0.12t = 2 or t = 16.67 NOT an integer
B 0.12t = 4 or t = 33.33 NOT an integer
C 0.12t = 8 or t = 66.67 NOT an integer
D 0.12t = 20 or t = 166.67 NOT an integer
E 0.12t = 45 or t = 375 INTEGER

Many thanks,
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by DanaJ » Fri Feb 27, 2009 7:51 am

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by carllecat » Fri Feb 27, 2009 8:23 am
Thanks a lot DanaJ!

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by Ian Stewart » Fri Feb 27, 2009 1:06 pm
I also posted a solution here, which might go into a bit more detail than the solution at the link above:

www.beatthegmat.com/difficult-t15709.html
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com

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by carllecat » Sat Feb 28, 2009 6:18 am
Ian Stewart wrote:I also posted a solution here, which might go into a bit more detail than the solution at the link above:

www.beatthegmat.com/difficult-t15709.html
Thanks a lot Ian, you made it very clear.

Cheers!