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Re: GMAT Diagnostic Test Question 33 [#permalink]
03 Oct 2012, 02:08

bb wrote:

GMAT Diagnostic Test Question 33 Field: word problems (mixture) Difficulty: 650

Rating:

A kilogram of nut mixture contains X% chestnuts and Y% walnuts and sells for $7.00/kg. If the ratio of chestnuts is increased by 50% so that the new mixture is sold for $8.00/kg, what is the price of a kg of walnuts?

A. $1.00 B. $2.50 C. $5.00 D. $7.50 E. $10.00

I hate to bump an old thread but isn't there an issue re. what it means to "increase a ratio by 50%"? "Increasing a ratio" by 50% would e.g. involve increasing a ratio of 2:3 to 1:1 (e.g. we go from 0.66*1.5 = 1). THAT is a 50% increase in a ratio. Using a plugging in numbers approach, a movement from a 40% / 60% mixture ratio to a 50% / 50% ratio would represent an increase in the ratio by 50%. Yet this cannot satisfy any of the answer choices. The (1.5X) to (1-1.5X) answer used by gmat tiger is potentially troublesome as it can lead to negative quantities for the Walnut side.

(d1) AX/100+B(100-X)/100=7 (d2) A1.5X/100+B(100-1.5X)/100=8 *substitute c/(c+w) with X/100, and w/(w+c) with (100-X)/100

(e1) A0.5X/100-B0.5/100=1 *subtract d1 from d2 (e2) 200=AX-BX (e3) 200+BX=AX

(f1) (200+BX)/100+B(100-X)/100=7 *substitute AX in d1 with e3 (f2) 700=200+BX+100B-BX (f3) 500=100B

(g1) B=5 *the price of a kg of w

To avoid ambiguity stem should have STATED that the "proportion" of c in the mixture OR that the ratio of c to the whole mixture IS increased by 50%.

Hope this helps!

Gotcha. Although it's worth pointing out that the text in the question isn't ambiguous - it's just plain wrong. Your amendments would correct it, however.

I wonder if Bunuel or Karishma can provide their ways to this problem... Admittedly, GMAT TIGER's way is fairly clear...just wonder if there is a more concise way. Thanks. _________________

There are times when I do not mind kudos...I do enjoy giving some for help

I wonder if Bunuel or Karishma can provide their ways to this problem... Admittedly, GMAT TIGER's way is fairly clear...just wonder if there is a more concise way. Thanks.

This question is removed from the database. _________________