How much water should the milkman add to milk purchased : GMAT Data Sufficiency (DS)
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# How much water should the milkman add to milk purchased

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03 Nov 2012, 07:46
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How much water should the milkman add to milk purchased by him for $20/- to get 50% profit? (1) He has 1 litre of milk. (2) He wishes to sell the diluted milk at$25 a litre.
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Re: How much water should the milkman add to milk purchased [#permalink]

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05 Nov 2012, 11:02
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monikaleoster wrote:
How much water should the milkman add to milk purchased by him for $20/- to get 50% profit? (1) He has 1 litre of milk. (2) He wishes to sell the diluted milk at$25 a litre.

I marked A. can anyone explain Why it is wrong

I'm happy to help with this.

Suppose we know only (A) ----- we know he bought 1 liter of milk for $20. We know he wants a 50% profit, which means making$30 in sales. What we don't know is how much he will charge for the milk he sells. If he sells the milk for $30/L, then he doesn't have to add any water, and he will make a 50%. If he sells the milk at$60/L, he could drink half of it, and sell the other half and still reap a 50% profit. I think you were assuming that the buying price and the selling price were the same ---- it would be very good preparation for your future, getting an MBA and after, to recognize that these two seldom are the same.

We need to know both how much milk and selling price, in order to answer the question. That's why (C) is the answer.

Does all this make sense?

Mike
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Re: How much water should the milkman add to milk purchased [#permalink]

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10 Jul 2013, 19:52
mikemcgarry wrote:
monikaleoster wrote:
How much water should the milkman add to milk purchased by him for $20/- to get 50% profit? (1) He has 1 litre of milk. (2) He wishes to sell the diluted milk at$25 a litre.

I marked A. can anyone explain Why it is wrong

I'm happy to help with this.

Suppose we know only (A) ----- we know he bought 1 liter of milk for $20. We know he wants a 50% profit, which means making$30 in sales. What we don't know is how much he will charge for the milk he sells. If he sells the milk for $30/L, then he doesn't have to add any water, and he will make a 50%. If he sells the milk at$60/L, he could drink half of it, and sell the other half and still reap a 50% profit. I think you were assuming that the buying price and the selling price were the same ---- it would be very good preparation for your future, getting an MBA and after, to recognize that these two seldom are the same.

We need to know both how much milk and selling price, in order to answer the question. That's why (C) is the answer.

Does all this make sense?

Mike

Mike,

Do you think this is real gmat Question as it has too many assumptions in DS ?
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Re: How much water should the milkman add to milk purchased [#permalink]

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11 Jul 2013, 13:47
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Mountain14 wrote:
Mike,
Do you think this is real gmat Question as it has too many assumptions in DS ?

Dear Mountain14,
I think the framing of the question may be a little too folksy for the GMAT, but the substance of the question is perfectly legitimate. For example, the question could easily re-phrased in terms of some sort of obscure scientific liquid that a scientist is going to reduce and sell at a profit --- that would be very GMAT-like, and the principles of solution would be identical. We don't know to know anything about the liquid, its use or how to handle it, in order to answer a question about diluting it to achieve a certain profit. I think the only real assumption is that water is free, which seems like a quite reasonable assumption to make.
Does this make sense?
Mike
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Re: How much water should the milkman add to milk purchased [#permalink]

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11 Jul 2013, 18:14
mikemcgarry wrote:
Mountain14 wrote:
Mike,
Do you think this is real gmat Question as it has too many assumptions in DS ?

Dear Mountain14,
I think the framing of the question may be a little too folksy for the GMAT, but the substance of the question is perfectly legitimate. For example, the question could easily re-phrased in terms of some sort of obscure scientific liquid that a scientist is going to reduce and sell at a profit --- that would be very GMAT-like, and the principles of solution would be identical. We don't know to know anything about the liquid, its use or how to handle it, in order to answer a question about diluting it to achieve a certain profit. I think the only real assumption is that water is free, which seems like a quite reasonable assumption to make.
Does this make sense?
Mike

I got what you mean.... Thanks...
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Re: How much water should the milkman add to milk purchased [#permalink]

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21 Aug 2013, 04:07
Following thing is not clear to me:
How can milkman earn 50% profit by selling at $60. I marked A as the answer. For option B: SP=$25. CP= $20. Profit will be only 25% . I do not have good understanding of mixture problems. So please explain how the two statements are together sufficient Intern Joined: 14 Mar 2013 Posts: 48 Location: United States Concentration: General Management, Leadership GMAT Date: 12-03-2013 WE: General Management (Retail) Followers: 0 Kudos [?]: 55 [1] , given: 119 Re: How much water should the milkman add to milk purchased [#permalink] ### Show Tags 19 Nov 2013, 14:09 1 This post received KUDOS anamika7 wrote: Following thing is not clear to me: How can milkman earn 50% profit by selling at$60.
I marked A as the answer.
For option B: SP= $25. CP=$20. Profit will be only 25% .
I do not have good understanding of mixture problems. So please explain how the two statements are together sufficient

The question asks how much water should the milkman add to milk in order to get extra $10. He is not selling by$60, he paid $20 for X liters of milk and will sell Y liters of the mix milk+water to get$10 profit (50% of $20). To answer this, you need to know how much milk he has and for how much he is going to sell the mix of milk+water. Only 1 or only 2 is not enough to answer, but using 1 and 2 together we can answer the question. Intern Joined: 03 Aug 2013 Posts: 1 Followers: 0 Kudos [?]: 0 [0], given: 12 Re: How much water should the milkman add to milk purchased [#permalink] ### Show Tags 06 Jan 2014, 19:02 mikemcgarry wrote: monikaleoster wrote: How much water should the milkman add to milk purchased by him for$20/- to get 50% profit?
(1) He has 1 litre of milk.
(2) He wishes to sell the diluted milk at $25 a litre. I marked A. can anyone explain Why it is wrong I'm happy to help with this. Suppose we know only (A) ----- we know he bought 1 liter of milk for$20. We know he wants a 50% profit, which means making $30 in sales. What we don't know is how much he will charge for the milk he sells. If he sells the milk for$30/L, then he doesn't have to add any water, and he will make a 50%. If he sells the milk at $60/L, he could drink half of it, and sell the other half and still reap a 50% profit. I think you were assuming that the buying price and the selling price were the same ---- it would be very good preparation for your future, getting an MBA and after, to recognize that these two seldom are the same. We need to know both how much milk and selling price, in order to answer the question. That's why (C) is the answer. Does all this make sense? Mike Hi Mike, As the price of water is not given, should we assume it as free of cost or should we opt option 'E'. Satish. Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7121 Location: Pune, India Followers: 2133 Kudos [?]: 13639 [0], given: 222 Re: How much water should the milkman add to milk purchased [#permalink] ### Show Tags 06 Jan 2014, 21:25 satishv80 wrote: mikemcgarry wrote: monikaleoster wrote: How much water should the milkman add to milk purchased by him for$20/- to get 50% profit?
(1) He has 1 litre of milk.
(2) He wishes to sell the diluted milk at $25 a litre. I marked A. can anyone explain Why it is wrong I'm happy to help with this. Suppose we know only (A) ----- we know he bought 1 liter of milk for$20. We know he wants a 50% profit, which means making $30 in sales. What we don't know is how much he will charge for the milk he sells. If he sells the milk for$30/L, then he doesn't have to add any water, and he will make a 50%. If he sells the milk at $60/L, he could drink half of it, and sell the other half and still reap a 50% profit. I think you were assuming that the buying price and the selling price were the same ---- it would be very good preparation for your future, getting an MBA and after, to recognize that these two seldom are the same. We need to know both how much milk and selling price, in order to answer the question. That's why (C) is the answer. Does all this make sense? Mike Hi Mike, As the price of water is not given, should we assume it as free of cost or should we opt option 'E'. Satish. The intent of this question is clear - water costs nothing. But, it is not specifically mentioned. An official question will mention "assume water is available free of cost". I have seen DS questions which specify the price of water too. Hence, I would not assume that water is available free of cost until and unless it is specifically mentioned. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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07 May 2015, 03:59
monikaleoster wrote:
How much water should the milkman add to milk purchased by him for $20/- to get 50% profit? (1) He has 1 litre of milk. (2) He wishes to sell the diluted milk at$25 a litre.

In this gmat like questions,what will be more appropriate choice C or E?
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07 May 2015, 09:34
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ssriva2 wrote:
monikaleoster wrote:
How much water should the milkman add to milk purchased by him for $20/- to get 50% profit? (1) He has 1 litre of milk. (2) He wishes to sell the diluted milk at$25 a litre.

In this gmat like questions,what will be more appropriate choice C or E?

Dear ssriva2,
My friend, I am happy to help. I see that there is a lot of discussion on this question, but not a solution. I will show it here.

Since you are asking about (C) vs. (E), I will assume that you recognize that each statement alone is insufficient. Also, note: we are assuming that water is free. I believe virtually everywhere in the world, tap water of these quantities, a liter or two, is essentially free. Yes, if I am going to build a housing development that will use millions of gallons daily, I need to think about water costs. If I am filling my liter water bottle from the tap, I don't need to think about water costs.

For this calculation, it will be helpful to think about rates, because this is similar to work rates:
http://magoosh.com/gmat/2012/gmat-work-rate-problems/

Let's consider both statements together. We know he has a liter of milk, so he has spent $20---that's his cost. To get a 50% profit, he would have to have a revenue of$30.
If he is going to sell the diluted milk at $25/L, then to make a revenue of$30, he would have to sell ($30)/($25/L) = (6/5) L = 1.2 L. Well, he has a liter of milk, so he need to add 0.2 liters of water so that he winds up with 1.2 L of the diluted milk. That would sell for $30, which would give him a 50% profit. With both statements combined, we can come to an exact numerical answer. Together the statements are sufficient. OA = (C). Actually, for a problem such as this, yes, it's important to understand how to work the full solution, but in a DS set-up it's also an important skill to recognize that one could find the numerical answer, without actually doing all the calculations. That's what was happening in many of the responses above. Understanding how to do the calculations is very important, but ultimately, mastery of GMAT DS involves seeing that one could do the full solution without having to do every step of it. Does all this make sense? Mike _________________ Mike McGarry Magoosh Test Prep Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7121 Location: Pune, India Followers: 2133 Kudos [?]: 13639 [4] , given: 222 Re: How much water should the milkman add to milk purchased [#permalink] ### Show Tags 07 May 2015, 19:43 4 This post received KUDOS Expert's post ssriva2 wrote: monikaleoster wrote: How much water should the milkman add to milk purchased by him for$20/- to get 50% profit?

(1) He has 1 litre of milk.
(2) He wishes to sell the diluted milk at $25 a litre. In this gmat like questions,what will be more appropriate choice C or E? PLEASE HELP! That is the problem - this is not a "GMAT-like" question. This is a question from the Indian CAT curriculum. Someone converted it into the DS format without thinking about what is suitable for GMAT. Even in the Indian CAT PS questions, the high quality sources ALWAYS mention - "assume water is available free of cost". You are not required to make this assumption even when you have to choose a definite answer so you already KNOW that water has to be assumed to be free. But here, in a GMAT DS question, they require you to make that assumption. Therefore, you don't need to worry about what you will do if you get this question in GMAT - because you won't. And if you insist on an answer - I would mark it as (E). As I wrote above, I have seen questions where they gave the cost of water (say, if he is adding bottled water) so I will not assume anything and mark it as (E). _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: How much water should the milkman add to milk purchased [#permalink]

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13 May 2015, 05:21
Hi Karishma,
Can you please walk me through how we can solve this problem using Scale method (which uses concept of weighted average.) and assuming water is available free of cost.

And is it possible to solve almost all mixture questions using scale method?
I am very weak in solving mixture problem. It would be great if you can tell me some trick or any algorithm to solve questions.

Thanks,
Tripti
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13 May 2015, 22:01
triptigahlot wrote:
Hi Karishma,
Can you please walk me through how we can solve this problem using Scale method (which uses concept of weighted average.) and assuming water is available free of cost.

And is it possible to solve almost all mixture questions using scale method?
I am very weak in solving mixture problem. It would be great if you can tell me some trick or any algorithm to solve questions.

Thanks,
Tripti

This is not a weighted average question. It is cost price, sale price and profit question. So you cannot solve it using scale method.
Cost price = $20 Profit = 50% Sale Price =$30

He sells 1 liter at $25 so to earn$30, he must have 30/25 = 1.2 liters of solution. Since he has 1 lt of milk, he should add 0.2 lits of water.

Check this post on the scale method: http://www.veritasprep.com/blog/2011/03 ... -averages/
and this for details on using w. avgs for mixture questions: http://www.veritasprep.com/blog/2011/04 ... -mixtures/
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Re: How much water should the milkman add to milk purchased   [#permalink] 13 May 2015, 22:01
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