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not by 9?

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not by 9?

by sanju09 » Sun Apr 11, 2010 11:43 pm
Which of the following numbers is evenly divisible by 2, 3, 4, and 5, but not by 9?
(A) 15,215
(B) 21,896
(C) 47,630
(D) 60,840
(E) 78,420
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by thephoenix » Mon Apr 12, 2010 12:32 am
IMO E

a is not div by 2
b is not div by 3
c is not div by 4
d is div by 2,3,4,5 and 9
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by ajith » Mon Apr 12, 2010 12:34 am
sanju09 wrote:Which of the following numbers is evenly divisible by 2, 3, 4, and 5, but not by 9?
(A) 15,215
(B) 21,896
(C) 47,630
(D) 60,840
(E) 78,420
Any number which is divisible by 2, 3, 4, and 5 will be divisible by 60

A, B, C are clearly not divisible by 60

D is divisible by 9 so D is ruled out

Which leaves us with E
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by harshavardhanc » Mon Apr 12, 2010 12:49 am
sanju09 wrote:Which of the following numbers is evenly divisible by 2, 3, 4, and 5, but not by 9?
(A) 15,215
(B) 21,896
(C) 47,630
(D) 60,840
(E) 78,420
as two of the divisors are 2 and 5, we need to look at the options which end with a zero. This gives us C, D and E.

divisibility rule for 4 says that last two digits be divisible by 4, this eliminates C.

divisibillity rule for 9 says that sum of all the digits be a multiple of 9.

Which leaves us with E, as D is divisible by 9 (sum =18 )
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