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Divisor of a

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by hk » Mon May 25, 2009 5:50 pm
If a and b are positive integers such that a/b = 2.86, which of the following must be a divisor of a?

A. 10
B. 13
C. 18
D. 26
E. 50
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by gmatplayer » Mon May 25, 2009 7:14 pm
Answer: E

Question is what is b?

Since a is an integer only one of the five values given for B gives 'a' an integer value, & other four values will not be integer.

Try multiplying 2.86 by all five value choices

2.86*50 = 143 (integer)
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Re: Divisor of a

by Ian Stewart » Mon May 25, 2009 7:51 pm
hk wrote:If a and b are positive integers such that a/b = 2.86, which of the following must be a divisor of a?

A. 10
B. 13
C. 18
D. 26
E. 50
a/b = 2.86
a/b = 286/100
a/b = 143/50

So,

50a = 143b

Now 143 is a divisor of the right side of this equation, so it must be a divisor of the left side of the equation - that is, 50a is divisible by 143 - and since 50 can't be divided by 143, a must be divisible by 143 = 11*13. So a must be divisible by 11 and 13; B.
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by gmatplayer » Mon May 25, 2009 8:18 pm
I apologize for incomplete answer, you are right
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pls explain...!!

by chintanjadwani » Wed May 27, 2009 10:36 pm
i used a pretty stupid technique(tho the answers came out right)
if u can pls explain..!

i jus divided 2.86 by 26 , so got 22.... now 26 and 22 further 2 as a common factor, so we get 13 and 11...!! (got the same numbers as Ian ;) .!!

so ..somehow i got the answer...but wat method is this..!!!
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Re: pls explain...!!

by dumb.doofus » Wed May 27, 2009 11:06 pm
chintanjadwani wrote:i used a pretty stupid technique(tho the answers came out right)
if u can pls explain..!

i jus divided 2.86 by 26 , so got 22.... now 26 and 22 further 2 as a common factor, so we get 13 and 11...!! (got the same numbers as Ian ;) .!!

so ..somehow i got the answer...but wat method is this..!!!
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