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Bunuel
If x is an integer and x + x^2 + x^3 is odd, which of the following must be even?

A. x
B. x^2
C. x^3
D. 3x
E. x + x^2

We are given that x + x^2 + x^3 = odd

We can factor out an x:

x(1 + x + x^2) = odd

Since the product of two odd numbers = odd number, x MUST BE odd. Since x is odd, x^2 MUST BE odd also. Since odd + odd = even, we see that only answer choice E, x + x^2, is even.

Alternate solution:

When the sum of three integers is odd, EITHER each one is odd OR two of them are even and one of them is odd. However, since any integer raised to a power has the same parity (the fact of being odd or even), x, x^2, and x^3 must be ALL odd. Since odd + odd = even, we see that only answer choice E, x + x^2, is even.

Answer: E
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If x is an integer and x + x^2 + x^3 is odd, which of the following must be even?

A. x
B. x^2
C. x^3
D. 3x
E. x + x^2

I solved for x to be odd and selected A. I want to shoot myself.
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Hello from the GMAT Club BumpBot!

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