Is the integer n a multiple of 15?

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Is the integer n a multiple of 15? [#permalink]

28 Apr 2010, 07:59

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Question Stats:

61% (01:43) correct

38% (00:33) wrong

based on 49 sessions

Is the integer n a multiple of 15?

(1) n is a multiple of 20
(2) n+6 is a multiple of 3.

[Reveal] Spoiler: OA

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Re: Is the integer n a multiple of 15? [#permalink]

28 Apr 2010, 08:10

zz0vlb wrote:

Is the integer n a multiple of 15?

(1) n is a multiple of 20
(2) n+6 is a multiple of 3.

[Reveal] Spoiler:

can someone give an example of this problem?

Statement 1: if n = 40 then answer is no, if n = 60 , answer is yes.
Thus not sufficient.

Statement 2: n+6 is a multiple of 3 => n + 6 = 3m => n = 3m -6

=> n = 3( m - 2) , now if 7 = 3, its true , if m = 4 not true.

thus not sufficient.

If you combine both , n is multiple of both 3 and 5(as multiple of 20)
=> n is multiple of 15.

Thus C
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Last edited by gurpreetsingh on 28 Apr 2010, 11:03, edited 1 time in total.

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Re: Is the integer n a multiple of 15? [#permalink]

28 Apr 2010, 11:00

Gurpreetsingh Thank you so much.

Last edited by zz0vlb on 28 Apr 2010, 11:07, edited 1 time in total.

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Re: Is the integer n a multiple of 15? [#permalink]

28 Apr 2010, 11:04

zz0vlb wrote:

Gurpreetsingh Thanks. but n + 6 = 3m => n = 3m +6 should be n= 3m-6 => 3(m-2)

yes right, that's typo error. I have updated my post.
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Re: Is the integer n a multiple of 15? (1) n is a multiple of 20 [#permalink]

12 Aug 2012, 04:45

I have one doubt for this question -Please help me to understand

1.n is a multiple of 20 ...I understand its not Sufficient

2.n+6 is a multiple of 3

considering n a multiple of 15 ,all possible multiples of 15 and +6 is always divisible by 3 ..So it should be sufficient ?
Not sure why OA- C ?

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Re: Is the integer n a multiple of 15? (1) n is a multiple of 20 [#permalink]

12 Aug 2012, 06:55

vishu1414 wrote:

It should be the other way around: any multiple of 15 plus 6 is a multiple of 3, but it's possible n+6 to be a multiple of 3 so that n not to be a multiple of 15. Consider n=3.

Is the integer n a multiple of 15?

(1) n is a multiple of 20. If n=20, then the answer is NO but if n=60, then the answer is YES. Not sufficient.
From this statement though notice that n must be a multiple of 5.

(2) n+6 is a multiple of 3. If n=3, then the answer is NO but if n=15, then the answer is YES. Not sufficient.
From this statement though notice that n must be a multiple of 3, since n+6=3q --> n=3(q-2).

(1)+(2) From above we have that n is a multiple of both 5 and 3, thus it must be a multiple of 5*3=15. Sufficient.

Answer: C.

Hope it's clear.
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Re: Is the integer n a multiple of 15? [#permalink]

16 Aug 2012, 22:32

1 statement tels us that there are at least 2*2*5 as prime factors in n, but we are not sure that 3*5 are among the prime factors - so insufficient.
2 statement indicates that n is a multiple of 3 so it could be 0, 3, 15 ... - not sufficient
1+2 statements, here we see that n is a number which has 2*2*5 and 3 in its primes, so it must be a multiple of 15!
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Re: Is the integer n a multiple of 15? [#permalink] 16 Aug 2012, 22:32

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