Hi excelingmat,

You've posted several questions from NCERT, but none of them appear to be written in proper GMAT 'style', so I have to ask: Are these meant to be taken as GMAT questions or are they more akin to general 'math' questions?

If you're training to take the GMAT, then you really should focus on GMAT-centric materials (and there are plenty to choose from).

GMAT assassins aren't born, they're made,
Rich
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Hi Rich,

This is meant to be taken as a GMAT question. I found this question to a be a little tricky, which is why I've posted it here.

HI excelingmat,

Just to clarify - is the 'source' of this question calling it a 'GMAT question' or are you just practicing with it as part of your studies?

GMAT assassins aren't born, they're made,
Rich
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i don't think it is a gmat style question.
look at the question stem, what does 3:1 stand for? this information is relevant somehow? i have re-read the question several times
what does it want?

Hi,
ofcourse, this Q is not a typical GMAT Q and also not properly replicated from source..
but still lets solve it..
2 actions have been done on the mix...
1)7:3 is converted into 7:5 mix..
2) half of the mix of 7:5 is converted in 3:1 by adding/replacement of 240l milk..

lets start with action (2) as more info is given there..
let the mix common ratio be 2x..
so total sol = milk:water=7*2x:5*2x
240 l milk is added to half of it to make it 3:1..
so (7x+240)/5x =3:1..
we get x=30 or 2x=60..
so the sol is 7*60:5*60=420:300..

now we look at the first action ..
this was created from 7:3 mix...
so say x was added to get this ratio...
so 420/(300-x)=7/3..
here x =120..
but 120 does not seem to be a choice..

now, let us do by replacement but that only makes the question complicated and unlike a GMAT question.
Initial Ratio- 7*2x:5*2x
240 litre milk is added while 240 l of mix is removed. In this 240 l of mix we remove 240*7/12 or 140 l of milk.
Thus, the final product has 240-140 or 100 litre milk added to it instead of 100 l of water.

(7x+100)/(5x-100)=3/1
7x+100=15x-300 or 8x=400 or 2x=100
So initial quantity = 7*100:5*100 = 700:500

Let us say that y is removed in initial quantity to get it to 7:3 ratio
Thus, 700/(500-y)=7/3 or 2100=3500-7y or y=200
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+1 for 120 as the answer..if the question is interpreted as is interpreted by chetan2u; other than that, worst wording.

Bunuel

This question should be removed because it unnecessarily consumes limited available time of GMAT students which does not appear to belong in GMAT syllabus. Also, the expert solution of this ques by chetan2u does not match with the answer choices.
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