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susha0df: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Tue Mar 19, 2013 3:03 am

by susha0df » Fri Mar 29, 2013 7:00 pm

i am not able to understand the solution given by PR - any pointers?

DS Qs-

If a and b are integers and a is even, what is the value of a - b?
(1) a < 3
(2) a/b=2/7

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Source: Beat The GMAT — Data Sufficiency | Fri Mar 29, 2013 7:00 pm

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Fri Mar 29, 2013 8:39 pm

susha0df wrote:
If a and b are integers and a is even, what is the value of a - b?
(1) a < 3
(2) a/b=2/7

Target question: What is the value of a - b?

Statement 1: (1) a < 3
Since we don't know the value of a or b, there's no way to find the value of a - b.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: a/b = 2/7
There are many pairs of values that meet this condition. Here are two:
Case a: a = 2 and b = 7, in which case a - b = -5
Case b: a = -2 and b = -7, in which case a - b = 5
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined:
There are still many pairs of values that meet this condition. Here are two:
Case a: a = 2 and b = 7, in which case a - b = -5
Case b: a = -2 and b = -7, in which case a - b = 5
Since we still cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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himu: Master | Next Rank: 500 Posts; Posts: 345; Joined: Sun Dec 21, 2008 10:57 pmFollowed by: 3 members; Thanked: 6 times

by himu » Sat Mar 30, 2013 12:25 am

+1 E

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susha0df: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Tue Mar 19, 2013 3:03 am

by susha0df » Sat Mar 30, 2013 12:42 am

Hi Brent,

thanks for your explanation - helps a lot.

So i guess when a qs simply says about even or odd integers - we should not limit to +ve integers. For A<3 and a is even, I was limiting myself to 0 and 2 as possible values of a and therefore coming up with a different solution.

cheers
Sushanta

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GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Sat Mar 30, 2013 5:02 am

susha0df wrote:
So i guess when a qs simply says about even or odd integers - we should not limit to +ve integers. For

Exactly. The test-makers often like to test whether or not students recognize that evens and odds extend to negative numbers, as well as zero being an even number.

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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