A 20% ethanol solution is mixed with another ethanol solution, say, S of unknown concentration in the proporti

Question

A 20% ethanol solution is mixed with another ethanol solution, say, S of unknown concentration in the proportion 1:3 by volume. This mixture is then mixed with an equal volume of 20% ethanol solution. If the resultant mixture is a 31.25% ethanol solution, then the unknown concentration of S is

Accepted Answer

50%. Let the volume of the first and the second solution be 100 and 300. When they are mixed, quantity of ethanol in the mixture = (20 + 300S) Let this solution be mixed with equal volume i.e. 400 of third solution in which the strength of ethanol is 20%. So, the quantity of ethanol in the final solution