1000DS Price of Magzines sold percent

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rookiez: Master | Next Rank: 500 Posts; Posts: 132; Joined: Thu Mar 26, 2009 7:53 pm; Location: Gurgaon; Thanked: 1 times

by rookiez » Sun Jul 05, 2009 10:32 am

11. If the price of a magazine is to be doubled, by what percent will the number of magazines sold decrease?
(1) The current price of the magazine is $1.00.
(2) For every $0.25 of increase in price, the number of magazines sold will decrease by 10 percent of the number sold at the current price.

OA is C
IMO B

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Source: Beat The GMAT — Data Sufficiency | Sun Jul 05, 2009 10:32 am

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

by DanaJ » Sun Jul 05, 2009 12:26 pm

1 is insufficient since you don't have any info on the algorithm of sales.

2 provides the following info: for each $0.25 price increase, the decrease will be 10% of the original sales figure. This can be "translated" into the following:

Say x is the original price of the magazine. If the price becomes x + 0.25*n, then the sales will drop by n*10%. To calculate the drop in number of magazines sold, all you have to do is find n.

Since we know that the price doubled, then we can establish that x + 0.25*n = 2x, meaning that 0.25*n = x. As you can see, unless you know x, then there's no way of finding n.

This is why you also need statement 1: with x = 1.00 = 0.25*n, n will be 4 and the decrease in number of magazines sold will be n*10% = 40%.

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