How much water should the milkman add to milk purchased

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...

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.

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.

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

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:
https://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

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: https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2011/0 ... -averages/
and this for details on using w. avgs for mixture questions: https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2011/0 ... -mixtures/