integers, number properties

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integers, number properties

by jopup » Tue Jun 17, 2008 2:02 pm

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by II » Tue Jun 17, 2008 3:04 pm
ok ... first analyse the question stem.
Key points:
n, p are integers. Nothing about whether they are positive or negative. So they can be either.
Question is asking whether p is positive ?
So you know this is a question which will be testing your positive/negative numbers knowledge.

Lets identify the easy statement.

Statement 1 here is the easy statement. We can draw the AD/BCE grid.
1) n+ 1 > 0
This is clearly insufficient to answer the question "is p > 0" because we have no information on p here. It states that n + 1 > 0, which means that n can be 0 (note: 0 is neither positive or negative) or it can be a positive number. We know that n CANNOT be a negative number.

So we cross out AD from our answer grid. We are left with answer choices BCE.

2) np > 0
So this tells us that 2 integers multiplied must be positive (>0). So this means that n AND p must both be negative (neg*neg = pos), or they must both be positive (pos*pos = pos).
Again, the information here is insufficient to determine whether p is positive.

So we can cross out answer choice B from our answer list. We are no left with C or E.

From 1) we know that n can never be negative, and from 2) we know that both n and p must have the same sign.
From this we can deduce that p must be positive, since n can never be negative.

So answer is C.

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by jopup » Wed Jun 18, 2008 8:42 am
i thought n could equal a negative fraction but i forgot n and p were both integers