Question

A 60 litre solution of alcohol and water contains 20litre ofalcohol.How much alcohol must be added to produce a solution of 50% alcohol.

Answer 1

Total mixture of alcohol and water =60 litre
quantity of alcohol in mixture =20litre
It must be 50 percent = 30 litre alcohol
alcohol required = 30 l - 20 l
10l

Answer 2

Let us assume that we add “a” litre of alcohol to the mixture 50%
So new qty. of alcohol = (20 + a ) litre
And new quantity if total mixture will be (60+a) litre
So new % of alcohol in the mixture would be quantity of alcohol in the morning mixture / total quantity
50% = (20+a)/ (60 + a); 50% is same as 50 / 100 or 0.5 or 1 by 2
0.50*(60+a) = (20 + a)
1 by 2 * 60 + 1 by 2 (a)
10 = 1 by 2 ( a )
=> a = 20 litre
So we have to add 20 litre of alcohol , so that total alcohol = 40 litre
And total quantity of mixture would be 60 + 20 = 80 litre , which means mixture will have 50% of alcohol as 40 litre is 50% of 80 litre