Conditional Reasoning doubt

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sreak1089: Master | Next Rank: 500 Posts; Posts: 379; Joined: Wed Jun 03, 2009 3:05 amFollowed by: 1 member; Thanked: 19 times; GMAT Score:690

by sreak1089 » Tue Jan 12, 2010 7:10 am

I have a doubt on Conditional reasoning problem that I studied in PowerScore CR.
Basically, it is about identifying Sufficient and Necessary condition.

Statement is: "People who excercise have an increased life span."

From the above statement we need to identify Sufficient and Necessary condition.

According to me "Sufficient condition" is "Increased Life Span" and necessary condition is "People must excercise".
Thus in PowerScore CR convetion, equation would be ILS --> E (ILS indicates Increased Life Span, E indicates People must excercise".

However, in the book, it is reverse, the Sufficient condition is identified as "People who excercise" and Necessary condition is identified as "Increased Life span". I am not able to understand why. Can any one, please clarify..

Source: Beat The GMAT — Critical Reasoning | Tue Jan 12, 2010 7:10 am

Testluv: GMAT Instructor; Posts: 1302; Joined: Mon Oct 19, 2009 2:13 pmFollowed by: 164 members; Location: Toronto; Thanked: 539 times; GMAT Score:800

by Testluv » Tue Jan 12, 2010 6:02 pm

Hi,

first of all, GMAT does NOT test conditional reasoning (the LSAT does).

So, really this is a waste of time for GMAT preparation.

Now, the statement reads:

"People who exercise have an increased life span."

Does this mean that all people who have long life spans exercise? Certainly not. Thus, having a long life span certainly isn't sufficient to conclude that you exercise. Therefore, long life-span is NOT the sufficient condition, and thus, must instead be the necessary condition.

The statement does guarantee that people who exercise have increased life spans. Thus, IF you exercise, THEN you increase your life-span. In other words, the sufficient condition is exercising while the necessary condition is increased life span.

Mixing up sufficiency and necessity is a very common error that LSAT novice students make, and that many LSAT wrong answers are. However, this is completely irrelevant for the GMAT.

Kaplan Teacher in Toronto

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