Hi all,
I'm a newbie here so I hope this is the right place to post. I wasn't sure how to derive the answer for the following question, and I hope someone here can help:
Q: If n is a positive integer, and the product of all integers from 1 to n is a multiple of 990, what is the least possible value of n?
A: 10 11 12 13 14
I know the answer is 11, but how do I get to the answer using an efficient method?
Thanks!
Question from GMAT sample test #1 (probably factors etc.)
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- Neo2000
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The Bold statement implies n factorialparadox wrote:
Q: If n is a positive integer, and the product of all integers from 1 to n is a multiple of 990, what is the least possible value of n?
A: 10 11 12 13 14
I know the answer is 11, but how do I get to the answer using an efficient method?
Thanks!
So n! = kx990 =k x 9x10x11
Hence 11 has to become the least value
- Neo2000
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- Posts: 519
- Joined: Sat Jan 27, 2007 7:56 am
- Location: India
- Thanked: 31 times
There definitely are numbers lower than 990 that will be factors of 990. However the question states that n! is a multiple of 990. Now 990 can be split into 9x10x11 with 11 being the highest prime. Therefore the only way you could get 11 in the product was if it was actually part of n.paradox wrote:Pardon my ignorance, but how do you know that there are no numbers lower than 11 in the sequence that could be factors of 990?
Therefore the smalles possible value of n had to be 11