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simple but twisted

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Source: — Data Sufficiency |
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Re: simple but twisted

by ssmiles08 » Fri Jul 03, 2009 6:55 am
sanjib wrote:If n is an integer, is n/15 an integer?
(1) 3n/15 is an integer.
(2) 8n/15 is an integer

Need explanation please.
For n to be divisible by 15, n needs to be divisible by at least one 3 and one 5.

1) tells us that n/5 is an integer. we don't know if n is divisible by 3. n can be 15 or n can be 20. Insufficient.

2) 8n/15 = integer. 8 is not divisible by 15, which means n must be divisible by 15 for (8n)/15 to be an integer. Since we know n/15 = integer in this statement, it is sufficient for answering the original question.

(B)
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by rahulg83 » Sat Jul 04, 2009 12:25 am
I don't agree
Consider 8n/15=1
n/15=1/8, which is not an integer

Again consider 8n/15=8
n/15=1, which is an integer

statement 2 is insufficient...

Statement 1 is also insufficient..

But if we combine both the statements, we know 3 and 8 don't have any common factors, for both of terms 8n/15 and 3n/15 to be integers, n/15 has to an integer.

Hence C..
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by ssmiles08 » Sat Jul 04, 2009 12:57 pm
rahulg83 wrote:I don't agree
Consider 8n/15=1
n/15=1/8, which is not an integer
rahulg83,

your statement for n/15=1/8 is not valid. 'n' has to be an integer as stated in the problem. here n = 15/8 which would not be an integer.
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by amitsahdev » Sat Jul 04, 2009 9:04 pm
I agree with ssmiles08, I did the question myself without looking at any replies and ended up with the same logic and same answer as ssmiles08...just looking at option B should tell u that its the answer...
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by rahulg83 » Sat Jul 04, 2009 9:31 pm
hmmm...thanks ssmiles..realized my mistake...
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