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Is x + y – z + t even?

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Is x + y – z + t even? [#permalink] New post 22 May 2012, 08:12
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A
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52% (01:53) correct 48% (01:07) wrong based on 83 sessions
Is x + y – z + t even?

(1) x + y + t is even
(2) tz is odd

why the answer is not C? as tz is odd, t and z both must be odd and and as x+y+t is even, even - odd = odd so C, can anyone please explain?
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Re: Is x + y – z + t even? [#permalink] New post 22 May 2012, 08:35
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gmihir wrote:
Is x + y – z + t even?
(1) x + y + t is even
(2) tz is odd

why the answer is not C? as tz is odd, t and z both must be odd and and as x+y+t is even, even - odd = odd so C, can anyone please explain?


Though i did not understand why the OA is E

i would go through my understanding, and SME can help me out here

given that x + y + t - z is even
so for this
two terms (x + y + t) & z
so to have a even result both the terms should be either even or both should be odd

E - E = E
O - O = E

1) info about x + y + t is even .. good for us, but no information about z is given , hence INSUFFICIENT

2) tz is odd

O * O = O
E * O = O
O * E = O

hence we cannot make sure if z is even or ODD, hence INSUFFICIENT

so the answer choices A, B, D are knocked off...

now taking together 1 & 2

x + y + t = even
and z is either even or odd
hence the answer is E
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Re: Is x + y – z + t even? [#permalink] New post 22 May 2012, 09:51
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gmihir wrote:
Is x + y – z + t even?

(1) x + y + t is even
(2) tz is odd

why the answer is not C? as tz is odd, t and z both must be odd and and as x+y+t is even, even - odd = odd so C, can anyone please explain?


Notice that we are not told that unknowns can only be integers.

Even when we consider the statements together we can have the following cases:
x+y=odd, t=odd and z=odd then (x+y)-z+t=odd-odd+odd=odd and the answer to the question is NO;
x+y=\frac{3}{2}, t=\frac{1}{2} and z=2 then (x+y)-z+t=\frac{3}{2}-2+\frac{1}{2}=0=even and the answer to the question is YES.

Two different answers. Not sufficient.

Answer: E.

Hope it's clear.
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Re: Is x + y – z + t even? [#permalink] New post 22 May 2012, 19:26
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Picked E. because we are not told that all digits are integers. So in that case it the the ans may not be an integer. And if it is not an integer it is also neither even nor odd.
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Re: Is x + y – z + t even? [#permalink] New post 24 May 2012, 06:51
harshavmrg wrote:
E * O = O
O * E = O


This is wrong.
Going by examples when you multiply the even(4)with the odd(3) the answer is 12 which is even.

hence whenever a Even is multiplied to a even or odd number it is always an even number. I hope you take note of this point.

Bunuel wrote:
Notice that we are not told that unknowns can only be integers.

This is one of the first points to try in such questions when nothing is mentioned about the type of numbers.
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Re: Is x + y – z + t even? [#permalink] New post 24 May 2012, 19:24
gmihir wrote:
Is x + y – z + t even?

(1) x + y + t is even
(2) tz is odd

why the answer is not C? as tz is odd, t and z both must be odd and and as x+y+t is even, even - odd = odd so C, can anyone please explain?


Hi,

Whenever you are trying to solve such type of question, do not direct assume all variables as integers (if it is not mentioned).

x,y,z & t can be any real number for which the above relationships are true.

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Re: Is x + y – z + t even? [#permalink] New post 24 May 2012, 20:18
true that cyberjadugar!
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Re: Is x + y – z + t even? [#permalink] New post 29 Jul 2014, 14:54
gmihir wrote:
Is x + y – z + t even?

(1) x + y + t is even
(2) tz is odd

why the answer is not C? as tz is odd, t and z both must be odd and and as x+y+t is even, even - odd = odd so C, can anyone please explain?

The question does not say that x,y,z,t are integers. They can be fraction also.
Re: Is x + y – z + t even?   [#permalink] 29 Jul 2014, 14:54
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