is X odd?

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neerajkumar1_1: Master | Next Rank: 500 Posts; Posts: 270; Joined: Wed Apr 07, 2010 9:00 amFollowed by: 2 members; Thanked: 24 times

by neerajkumar1_1 » Tue Sep 07, 2010 9:31 pm

is X odd ?

a) 2x-1 is odd

b) X^3 is odd

I guess this question has been discussed before and I am also quite happy with Kaplan's explanation...

What I need to confirm is: Do we consider numbers like 1.33 or 3.5 as odd????

Also essentially i want to make my concept clear on this question as i had selected answer to be B....

So I hope u guyz can provide me with a solution which could clear my fundas...

thanks a ton...

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Source: Beat The GMAT — Data Sufficiency | Tue Sep 07, 2010 9:31 pm

roh00kan: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Thu Oct 30, 2008 10:36 pm; Thanked: 3 times

by roh00kan » Tue Sep 07, 2010 11:01 pm

In GMAT "value" of a number depends on the statements.

In Math, if a number has anything after 'decimal', then that number is considered to be a real number, not a whole or an integer number. Therefore, even or odd designation can only apply to integers. This is specifically applied in scientific programming, especially in FORTRAN. For example: 1.0 is a real number, not an odd integer in FORTRAN.

If you check the definition for even and odd, you will find that: If we divide a number by 2 and if remainder remains 0, then that number is even and if the remainder is 1, then that number is odd. So we can have -ve even or odd numbers. But not 1.333 as odd and 2.2 as even.

Hope this is clear.

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beatthegmatinsept: Master | Next Rank: 500 Posts; Posts: 422; Joined: Mon Aug 09, 2010 11:47 amFollowed by: 1 member; Thanked: 22 times; GMAT Score:680

by beatthegmatinsept » Wed Sep 08, 2010 9:04 am

A should be enough too here, isnt it?

Being defeated is often only a temporary condition. Giving up is what makes it permanent.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

by Stuart@KaplanGMAT » Wed Sep 08, 2010 9:15 am

beatthegmatinsept wrote:A should be enough too here, isnt it?

No, (1) isn't sufficient alone.

If 2x - 1 is odd, then:

2x = odd + 1

2x = even

x = even/2

Since dividing an even number by 2 can generate both odd and even integers (6/2 = 3; 8/2 = 4), (1) gives both a "yes" and a "no" answer to the question.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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