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# I'm having some issues with questions about multiples,

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Intern
Joined: 08 Jul 2009
Posts: 6

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23 Jul 2009, 16:17
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I'm having some issues with questions about multiples, clearly.

Is the integer n a multiple of 15?
1) n is a multiple of 20
2) n + 6 is a multiple of 3

I'm not understanding how they got to the OA, which is C.

Senior Manager
Joined: 04 Jun 2008
Posts: 286
Re: Is n a multiple of 15? [#permalink]

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23 Jul 2009, 20:05
stmt1
n must be a multiple of 3 and also of 5 , but 20 is just 4 and 5, we dont know about 3.

stmt 2
n+6 is divisible by 3 - not sufficient

combine
consider all multiples of 20, such that n + 6 is divisible by 3.
20 + 6.....not divisible by 3
40 + 6.... no....40 not by 15
60 + 6..... yes, also 60 is divisible 15

another way: also, a multiple of 20 will be divisible by 5
further, if n+6 is divisible by 3, n is also divisible by 3, so it is also divisibly by 15.
Manager
Joined: 10 Jul 2009
Posts: 150
Re: Is n a multiple of 15? [#permalink]

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23 Jul 2009, 20:40
For n to be a multiple of 15 it should be a multiple of both 3 & 5

from 1)

n is a multiple of 20 -> n is a multiple of both 5, 2^2

from 2)

n + 6 is a multiple of 3
that implies n is a multiple of 3

combining 1 and 2 we get to know n is multiple of 3,5, 2^2
Re: Is n a multiple of 15?   [#permalink] 23 Jul 2009, 20:40
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