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og math # 37

by resilient » Tue Feb 05, 2008 8:21 pm
if positive integer n is divisible by and 7, then n must also be divisibile by which of the following.?

I. 12
II. 35
III. 70



Answer I is out of the question since n is a multiple of 35. However, why is choice III 70 wrong.
QA is C
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by Stuart@KaplanGMAT » Tue Feb 05, 2008 9:10 pm
Some of the question is missing, as are the answer choices.
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sorry

by resilient » Tue Feb 05, 2008 9:44 pm
if positive integer n is divisible by 5 and 7, then n must also be divisibile by which of the following.?

I. 12
II. 35
III. 70



a. none
b.I only
c. II only
d.I and II
e. II and III

Answer I is out of the question since n is a multiple of 35. However, why is choice III 70 wrong.
QA is C
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by simplyjat » Tue Feb 05, 2008 9:58 pm
The difference is between CAN BE and MUST BE...
n can be divisible by 70, whereas n must be divisible by 35
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SUBTLE DIFFERENCE

by resilient » Tue Feb 05, 2008 10:29 pm
THANKS FOR THE INFO.. ITS THESE TYPES OF SUBTLE DIFFERENCES THAT GET ME.
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by Stuart@KaplanGMAT » Wed Feb 06, 2008 11:24 am
simplyjat wrote:The difference is between CAN BE and MUST BE...
n can be divisible by 70, whereas n must be divisible by 35
Correct!

You always need to read the question carefully to determine exactly what it is that you're looking for.

If our number is a multiple of 5 and 7, we know it has to be a multiple of 5*7 as well (since they're both primes). Therefore, the minimum value of n is 35.

n could be any other multiple of 35, but since that's not what the question is asking, only II is a MUST be true: choose (c).
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