dave13 wrote:

chetan2u wrote:

Hi..

you have gone wrong in taking base of weighted average..

you are looking for % of entire mixture and that will be 40-25..

x will be less as 30 is closer to y(25) so x will be 30-25..

ans \(\frac{30-25}{40-25}=\frac{5}{15} = 1/3 = 33.33\)%

Hope it helps

Many thanks

chetan2u for reply and explanation!

one question: can you please elaborate on this ---> " you are looking for % of entire mixture and that will be 40-25 " yes % of the entire mixture why are you subracting 25 from 40

shouldnt it be 40%+25% = 30

i followed the paatern as explained here in this question (extrac:ted from the link above)

“Mixture A is 20 percent alcohol, and mixture B is 50 percent alcohol. If the two are poured together to create a 15 gallon mixture that contains 30 percent alcohol, approximately how many gallons of mixture A are in the mixture?

Can you say anything about the relative value of V1 and V2? Can you say which one will be greater? We discussed in the previous post that when we find the weighted average of two quantities, the average is closer to the one which has higher weight because that quantity ‘pulls’ the average toward itself. So if the new mixture contains 30% alcohol, which of the two mixtures – A (20% alcohol) or B (50% alcohol), will have higher volume? Obviously A because it pulled the average toward itself. The average, 30% alcohol, is closer to 20% than to 50%. Now, let’s calculate exactly how much of the 15 gallons was mixture A and how much was mixture B.

Hi..

here we have common item between the two mix as ryegrass..

it is 40% in X and 25% in Y... the mix gets it to 30%..

1) first point is if both were equal, the average would be 40+25/2=33.5%....... But here it is 30% and 30% is closer to 25%, so Y is MORE than X..

2) what is the difference between ryegrass separately - it is 40%-25% = 15%..

And WHAT is X doing to Mix - it is getting Y up from 25% to 30%, so it is COVERING the 5% of the earlier difference 15% and that is WHY its ratio is 5/15..

_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

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