Mixtures2

Ratio of 25% / Ratio of 40% = 40-35/35-25 = 1/2

So 1 part of 25% solution is added to 2 parts of 40% soln to from a 35% solution.

Hence 1/3 of the 40% must have been removed

I still don't get it. Can someone please provide a detailed explanation.

I was able to solve it by way of backtracking. Not ideal but at times gets the work done.

I started by choosing C. So if both the new solution and the old one are 50 percent each. Then the concentration is 20ml ( from the non substituded solution, 50ml * 0.40 ) + 12.5 ml ( from the substitued, 50ml * 0.25 ) .

Final concentration is (20+12.5)/100 which is 32.5. So its slightly less than final intended result. So we should substitute a bit less. Hence, Answer Choice B.

Even though I could get the answer this way, I would like to know the exact math involved.

I think Mitch has explained it very well here

https://www.beatthegmat.com/mixture-prob ... 12440.html

enjoylife1788 wrote:I still don't get it. Can someone please provide a detailed explanation.