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integers n and p

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integers n and p

by coffee5251 » Sun Jan 04, 2009 5:43 pm
If n and p are integers, is p > 0?

1. n+1 > 0

2. np > 0

OA C

I don't understand why the answer isn't B. If np > 0 doesn't that mean p > 0/n, which is p > 0? What am I missing?

Thanks for your help.
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by dmateer25 » Sun Jan 04, 2009 5:47 pm
2. np > 0

You can plug in some numbers to see why this statement isn't sufficient.

Let's say n=1 and p=1

1(1) = 1

and 1>0 so this satisfies the statement and p would be greater than 0.

Now we can also try n=-1 and p=-1

(-1)(-1) = 1

and 1>0 so this satisfies the statement and p would be less than 0.


Therefore, statement 2 is insufficient.
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by cramya » Sun Jan 04, 2009 5:55 pm
I don't understand why the answer isn't B. If np > 0 doesn't that mean p > 0/n, which is p > 0? What am I missing
np > 0 means n and p are both positive or both negative. Stmt II does not tell us which case it is.

Stmt I

n+1 > 0
n>-1

n could be 0,1,2......

No info on p

Combined

n>-1
np>0

Since n is an integer n cant be 0 since np>0 so n has to be positive. If n is positive p has to be positive since np>0

Suff

Choose C)

Hope this helps also in addn to what Dmateer posted.
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by cramya » Sun Jan 04, 2009 5:58 pm
Hi Coffee,

Friendly request :Please post data sufficiency questions in the appropriate section of this forum.

Regards,
Cramya
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by coffee5251 » Sun Jan 04, 2009 6:13 pm
Thanks for your help. Sorry about posting in the wrong forum- I hadn't even realized I'd done that. Oops
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by calcpa2012 » Sun Sep 18, 2011 9:04 am
Ah i GET IT
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by sl750 » Sun Sep 18, 2011 11:23 am
coffee5251 wrote:If n and p are integers, is p > 0?

1. n+1 > 0

2. np > 0

OA C

I don't understand why the answer isn't B. If np > 0 doesn't that mean p > 0/n, which is p > 0? What am I missing?

Thanks for your help.
you cannot divide by n here unless you are sure that it a positive number. Here it could be negative, that could change the sign, so you cannot perform such an operation
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