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Re: GMAT Diagnostic Test Question 33 [#permalink]
04 Nov 2010, 10:39

GMAT TIGER wrote:

Explanation

Rating:

Official Answer: C

Weight of chestnut = x% of 1 kg Price of chestnut = A Weight of walnut = y% of 1 kg = (1-x)% of 1 kg Price of walnut = B

XA + (1-X) B = 7 ……………………….i (1.5X) A + (1 - 1.5X) B = 8 …………….ii

From 1 and 2: 0.5XA – 0.5XB = 1 XA – XB = 2 XA = 2 + XB…………………………… iii

Substitute the value of XA on Equation i: XA + (1-X) B = 7 2 + XB + B - XB = 7 B = 7 - 2 B = 5.00

Therefore, it is C.

The Question says nowhere that Walnut and Chestnut are the only nuts in the mixture.We must then introduce two more constants for Percentage and Price of Rest of mixture.

Assuming that chestnuts and walnuts only are available in the mixture,we would require either one of the percentages of Walnut or Chestnut. _________________

Argument : If you love long trips, you love the GMAT. Conclusion : GMAT is long journey.

What does the author assume ? Assumption : A long journey is a long trip.

Re: GMAT Diagnostic Test Question 33 [#permalink]
06 Aug 2011, 12:12

I'm not entirely convinced with the solution.

Chestnuts = C% and Walnuts = w% 50% increase in Chestnuts (c) prompted a price rise of $1. therefore, the original chestnut percentage C% should be $2. so, the original walnut percentage W% costs $5.

As far as walnuts are concerned, W% of 1kg cost $5. Therefore, by proportion, 1kg of walnuts will cost (5*100/W).

The price of 1 kg of walnuts can't be calculated based on the current information.

Where do you think I am going wrong with my line of thinking?

Re: GMAT Diagnostic Test Question 33 [#permalink]
01 Oct 2011, 03:25

I take issue with the wording of this question. First off, it says that the mix contains x% chestnut and y% walnut, but does NOT indicate that these are the only ingredients in the bag. Therefore, the immediate conclusion that y=1-x is, in my opinion, not usable. And, based on the nature of questions in the GMATQ, it becomes instinctual to be on your guard against small details like that.

Also, it says that the ratio of chestnuts is increased by 50%, but this is itself vague. The ratio of chestnuts to what? If you assume the ratio of chestnuts to the entire mix, then yes, it would be appropriate to assume 1.5x chestnuts and proceed accordingly. But I wasted about 5 minutes wondering if the statement was referring to the ratio of chestnuts to walnuts, which became an arithmetic nightmare. Imagine the original ratio of chesnuts to walnuts is r=x/y, so increasing that ratio implies that our new mix has 1.5r=x/y. You can see how a test taker might be unable to do much with this.

I'd be less nit picky if the GMAT consistently overlooked such things, but it is typical of GMAT questions to trap test takers on details as small as this.

Re: GMAT Diagnostic Test Question 33 [#permalink]
18 Jan 2012, 07:47

In my opinion, the wording is a little ambiguous. It states the mixture contains X% of Chestnuts and Y% of Walnuts - but it doesnt explicitly state those are the only ingredients. What if there were another Z% of hazelnut? You couldnt use the Y = 1-X trick then and it would not be solvable.

Re: GMAT Diagnostic Test Question 33 [#permalink]
01 Feb 2012, 07:45

Guys! I have arrived at the answer ( C ) in the following way:

If 50% increase of the chestnuts is causing a $1 change in total cost of the mixture, then 100% of chestnut inside the mixture costs us $2. So, The cost of the walnut in the mixture is ($7 - $2) or $5.

But, then I pause thinking that this $5 cost of walnuts should be the cost for less than 1 KG of walnuts (because, the mixture itself is 1 KG). But the question is asking "what is the price of a kg of walnuts"

So, IMO, the question should ask, instead, WHAT IS THE COST OF WALNUTS IN THE MIXTURE.

Re: GMAT Diagnostic Test Question 33 [#permalink]
01 Feb 2012, 09:26

I concur the notion that this problem was extremely hard for "only" a 650 rating. Although the logic and reasoning was easy to deduce, having to use a systems of equations with variables given in percentages seemed to be quite messy and challenging ...

can a moderator put up a satisfactory explanation to the problem. this seems to have been hanging for too long now.

kindly clarify all details ( increase walnut ratio / price in mixture / etc.. )

help is much appreciated.. _________________

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GmatPrep1 [10/09/2012] : 650 (Q42;V38) - need to make lesser silly mistakes. MGMAT 1 [11/09/2012] : 640 (Q44;V34) - need to improve quant pacing and overcome verbal fatigue.