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Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
19 Mar 2013, 17:05

1

This post received KUDOS

GMAThirst wrote:

If xy > 0 and yz < 0, which of the following must be negative:

A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2)

xy > 0 ++ (or) -- yz < 0 +- (or) -+

Remember Square of any number is always +ve. so we can remove all squares

A. xyz there is a chance for --+ so may be + B. xy ++ or -- C. xz if x is + then z should be - and vice versa D. x may be + or - E. +ve _________________

GMAT - Practice, Patience, Persistence Kudos if u like

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
29 Aug 2013, 04:36

I also follow the table approach for these types of questions, as per the attached file. I set up the columns for x, y, and z, and check which combination of positive and negative values I need to satisfy the conditions given (xy>0 and yz<0), then I check each answer choice in turn. When actually doing these questions I wouldn't fill in the whole table (since the answer is C there is no point checking D and E), but for the sake of completeness I added them. Hope it helps a bit, I'm more visual so didn't either consider the algebraic approach given above!