Fractions odd or even - Kaplan - The Beat The GMAT Forum - Expert GMAT Help & MBA Admissions Advice

Fractions odd or even - Kaplan

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venmic: Master | Next Rank: 500 Posts; Posts: 222; Joined: Mon Oct 13, 2008 4:04 pmFollowed by: 2 members; Thanked: 3 times

by venmic » Sat Aug 07, 2010 8:30 am

is X odd

a) 2x-1 is odd

b) X^3 is odd ..

fractions are not odd or even so how can the answer by even or odd

This is a kaplan question

This question can be applied only to integers so if it is an integer then the answer should be D but the answer here is E
how is that possible
even and odd concept can never be applied to fraction

Will be nice if I can get a good explaination on this

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Source: Beat The GMAT — Data Sufficiency | Sat Aug 07, 2010 8:30 am

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

by selango » Sat Aug 07, 2010 8:52 am

x is odd?

stmt1,

2x-1 is odd

x=1,2x-1 is odd,x is odd

x=2,2x-1 is odd,x is even

Insuff

stmt2,

x^3 is odd-->x is odd

Odd*Odd*Odd=Odd.

x can be odd integer or cube root of an odd integer

InSuff

Combining 1 and 2,

If x is an integer only,2x-1 can be odd.

x is an integer-->x^3 is odd

-->x is odd

suff

Pick C

Last edited by selango on Sat Aug 07, 2010 9:59 am, edited 1 time in total.

--Anand--

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Sat Aug 07, 2010 9:16 am

The answer should be E.

for case 2

consider a real number [3^(1/3) ] , it cube is going to be 3, but the number itself is not ODD.

consider a number 27 its cube is odd, the number itself is also odd...

thus choice is insufficient.

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venmic: Master | Next Rank: 500 Posts; Posts: 222; Joined: Mon Oct 13, 2008 4:04 pmFollowed by: 2 members; Thanked: 3 times

by venmic » Sat Aug 07, 2010 9:48 am

consider a real number [3^(1/3) ] , it cube is going to be 3, but the number itself is not ODD.

you mean --> cube root of 3 right ???

are we saying that is not odd

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

by selango » Sat Aug 07, 2010 9:59 am

arora,

Edited my post..Do u agree with the solution..

--Anand--

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Sat Aug 07, 2010 11:18 am

venmic wrote:consider a real number [3^(1/3) ] , it cube is going to be 3, but the number itself is not ODD.

you mean --> cube root of 3 right ???

are we saying that is not odd

yes cube root of 3

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Sat Aug 07, 2010 11:22 am

selango wrote:x is odd?

stmt1,

2x-1 is odd

x=1,2x-1 is odd,x is odd

x=2,2x-1 is odd,x is even

Insuff

stmt2,

x^3 is odd-->x is odd

Odd*Odd*Odd=Odd.

x can be odd integer or cube root of an odd integer

InSuff

Combining 1 and 2,

If x is an integer only,2x-1 can be odd.

x is an integer-->x^3 is odd

-->x is odd

suff

Pick C

I am just wondering if i can select x=Zero
which would mean that 2x -1 would be -1
and wont fit in choice 2.....

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

by selango » Sat Aug 07, 2010 11:34 am

We cannot choose x=0 as value of x must satisfy both equations..

--Anand--

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arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Sat Aug 07, 2010 11:45 am

selango wrote:We cannot choose x=0 as value of x must satisfy both equations..

you are right... it should be C...

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kvcpk: Legendary Member; Posts: 1893; Joined: Sun May 30, 2010 11:48 pmFollowed by: 7 members; Thanked: 215 times

by kvcpk » Sat Aug 07, 2010 12:16 pm

venmic wrote:is X odd

a) 2x-1 is odd

b) X^3 is odd ..

a) 2x-1 is odd
let x= 1 is odd
2x-1 = 1 is odd
Let x = 2 is even
2x-1 = 3 is odd
INSUFF

b) x^3 is odd
Let x=3..ODD
x^3 = 27..ODD
Let x = 3^1/3.. NOT ODD
X = 3..ODD
INSUFF

Combining:
2X-1 is odd and x^3 is odd
2x -1 = 2p+1 where P is integer
x = P+1 -> Implies integer+1
Hence X is integer.
If integer^3 is odd, Integer should be odd.
hence C

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