GMAT Prep / Number Properties
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Question: Is x+y+2z even (2z is always even)
Stmt I
x+z is even (we know x is even and y is even)
No info about y (If y is odd and if both x and z are even the sum would be odd (or) If y is even then x+y+2z will be even
INSUFF
Stmt II
y+z is even
Similar explanation as above apllies to x as it applied to y
INSUFF
Stmt I and II
x+z is even
y+z is even
Add both we get x+z+y+Z ios even (since even+even = even)
= x+y+2z which is what we need ot find Therefore its even
SUFF
C)
Stmt I
x+z is even (we know x is even and y is even)
No info about y (If y is odd and if both x and z are even the sum would be odd (or) If y is even then x+y+2z will be even
INSUFF
Stmt II
y+z is even
Similar explanation as above apllies to x as it applied to y
INSUFF
Stmt I and II
x+z is even
y+z is even
Add both we get x+z+y+Z ios even (since even+even = even)
= x+y+2z which is what we need ot find Therefore its even
SUFF
C)

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@cramya,
i see what you did but i thought it was E because of the following 
x + z = even
so it could be odd + odd or even + even
y + z = even
so it could be odd + odd or even + even
seeing that, x and y could both be odd or even. so for x + y + 2z to be even, x and y both have to be even, and we can't conclude that.
what are the mistakes i made?
i see what you did but i thought it was E because of the following 
x + z = even
so it could be odd + odd or even + even
y + z = even
so it could be odd + odd or even + even
seeing that, x and y could both be odd or even. so for x + y + 2z to be even, x and y both have to be even, and we can't conclude that.
what are the mistakes i made?
Seeing that, x and y could both be odd or even. so for x + y + 2z to be even, x and y both have to be even, and we can't conclude that.
what are the mistakes i made?
In x+z both could be odd or both even(one odd /other even not possible)
In y+z both could be odd or both even
x+z+y+z (this is nothing but x+y+2z)
odd+odd+odd+odd
= even
or
x+z+y+z(this is nothing but x+y+2z)
even+even+even+even
= even
Hope this helps!