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Bunuel
For all integers a and b, the operation θ is defined by \(aθb = \frac{a + b}{2}\). If x and y are integers, is \(x θ y\) an integer?


(1) \(x^2 = y^2\)

(2) \(x = –y\)


DS20593


Can someone find my flaw in thinking please?

Let us assume 1: in such case, x could be 1 and y -1, still satisfying (1). In such case, original question is not an integer. However, if we assume 1/1, then original question is an integer =1.


EDIT: DISREGARD. My flaw was in the assumption that a neutral integer would make the original question wrong lol. 0 still satisfies. silly me!
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Bunuel
For all integers a and b, the operation θ is defined by \(aθb = \frac{a + b}{2}\). If x and y are integers, is \(x θ y\) an integer?


(1) \(x^2 = y^2\)

(2) \(x = –y\)


Since only even numbers are divisible by 2, this question can be rephrased as "is x+y even?". Remember that zero is an even number.

S1: x and y can be zero, the same number with the same signs or the same number with opposite signs. Regardless, x+y will always be zero or another even number. SUFFICIENT.

S2: This is only true x and y = 0. SUFFICIENT.

ANSWER: D
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(x+y)/2 = int?

Given that x and y are integers, the only thing that won't make x+y/2 an integer is if x+y is odd

1. x^2 = y^2

Irrespective of whether x is positive or negative or whether y is positive or negative, we know that their squares equal each other, so worst case:
x+y = 0 i.e. even therefore 0/2 = 0 -->true

any number will work since we know x must equal at least the negative equivalent of y, therefore either Odd+ odd = even or even + even = even

sufficient

2. same logic
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Hello from the GMAT Club BumpBot!

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