more algebra!

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more algebra!

by vscid » Mon Dec 22, 2008 9:11 am
If x, y, z are integers, is x(y^2 + z^3) even?

1] x is odd.
2] The product xyz is odd.
The GMAT is indeed adaptable. Whenever I answer RC, it proficiently 'adapts' itself to mark my 'right' answer 'wrong'.

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Re: more algebra!

by parallel_chase » Mon Dec 22, 2008 9:44 am
vscid wrote:If x, y, z are integers, is x(y^2 + z^3) even?

1] x is odd.
2] The product xyz is odd.
Question stem: if x(y^2 + z^3) is even

either x is even and y can be either even or odd or z could be either even or odd, or all x y & z are odd.

Statement I
x is odd, we dont know anything y or z

if x is odd, y and z are also odd, then entire expression is even, because odd+odd = even

if y is even and z is odd or vice versa, then odd+even = odd, the entire expression becomes odd.

Insufficient.

Statement II

xyz = odd

this means x is odd, y is odd & z is odd

odd ( odd+odd) = odd* even = even, since odd+odd = even

Sufficient.

Hence, B.
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