Integer

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billyr: Senior | Next Rank: 100 Posts; Posts: 41; Joined: Tue Dec 16, 2008 11:53 pm

by billyr » Wed Feb 25, 2009 10:14 pm

A certain list consist of several different integer. Is the product of all integer in the list is positive?

(1) The product of the greatest and smallest in the list is positive
(2) There is an even number of integer in the list

The answer is c(need both statement), but why c?

Thanks

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Source: Beat The GMAT — Data Sufficiency | Wed Feb 25, 2009 10:14 pm

DanaJ: Site Admin; Posts: 2567; Joined: Thu Jan 01, 2009 10:05 amFollowed by: 550 members; Thanked: 712 times; GMAT Score:770

by DanaJ » Wed Feb 25, 2009 11:10 pm

Here's how I see it:
1. tells us that (smallest)*(greatest) is positive means that:
a. both are positive and since they are the "ends" of the series, that makes all the numbers positive. In this case, the product will be positive
b. both are negative, making all of the numbers negative. However, in this case we cannot tell if the product is positive, since we don't know if we have an even or an odd "number" of numbers. Take for example: -5, -4, -3. While it's true that (-5)*(-3) is positive, that cannot be said about the product of the three.

2 doesn't help much. All numbers could be positive, or you could have smth like: -5, 3, 4, 5.

Put the two together and you "eliminate" that weak spot in case b from stmt 1: even if all numbers are negative, they "cancel" each other's minuses. So the OA is ok.

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crazy4gmat: Master | Next Rank: 500 Posts; Posts: 160; Joined: Fri Aug 22, 2008 4:54 am; Thanked: 5 times; GMAT Score:660

by crazy4gmat » Thu Feb 26, 2009 9:53 am

gr8 expln.

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