Odd or not

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anticipation: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Mon Oct 26, 2009 4:52 am

by anticipation » Mon Sep 06, 2010 5:55 am

If y and z are integers, is y Ã— (z + 1) odd?

(1) y is odd
(2) z is even

[spoiler]OA: C[/spoiler]
[spoiler]
Why can't i plugin either of them as zero ? In that case, OA should E. Any inputs to correct my thought process would be great ?[/spoiler]

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Source: Beat The GMAT — Data Sufficiency | Mon Sep 06, 2010 5:55 am

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon Sep 06, 2010 6:50 am

Combining 1 and 2,

y is odd and Z is even

Note that 0 is an even integer.you can plugin the value only for Z.

sub z=0

y(z+1) = y*(0+1)=y

Since y is odd,y(z+1) is odd.

--Anand--

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anticipation: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Mon Oct 26, 2009 4:52 am

by anticipation » Mon Sep 06, 2010 7:14 am

selango wrote:Combining 1 and 2,

y is odd and Z is even

Note that 0 is an even integer.you can plugin the value only for Z.

sub z=0

y(z+1) = y*(0+1)=y

Since y is odd,y(z+1) is odd.

Thanks for ur inputs. Key here is to know that 0 is even , which I didnt know

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gopal.b: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Mon Sep 06, 2010 10:04 pm

by gopal.b » Mon Sep 06, 2010 11:05 pm

I could relate to your confusion.

From what I have known since school and also in studies of pure mathematics even and odd numbers were defined by convention only for natural numbers.
Which would mean zero is neither even nor odd and so are all -ve integers.
BUT
the GMAT considers even and odd to be defined for all integers.

All integers of the form 2n where n is an integer are even and all integers of the form 2n+1 where n is an integer are odd.

Which would make 0 even and -2 even and -1 -3 etc odd.

Regards,
Gopal[/quote]

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