Why a:c and b:c are added in the ratio 2:1??

Hi Sourav,

There can be different ratios for which the final concentration is 40%. In this question, we have to find among the options the ratio which yields in 40% concentration. Here, with the help of a & c and b & c, we have prepared 2 solutions which have 40% concentration. Adding these 2 mixtures in any ratio would yield a 40% concentration solution. But, we have to check which of the options suit. So, when we add them in 2:1 ratio, we get option A. Other options cannot be obtained.

Hope this answers your query.