Question

How much pure alcohol must be added to 400ml of 15 % solution to make it's strength 32% ?

Answer 1

400ml has 15% alcohol i.e 60ml . This means we have 340ml of water or the liquid with which alcohol is mixed
Let V be the volume of alcohol added to make the strength 32%
then V/340+V = 32/100. solving this we get V as 160ml

so we need to add 160 -60 = 100ml of alcohol

Answer 2

Let x = the required number of milliliters of pure alcohol.


Then we have:

400(15%) + x(100%) = (400+x)(32%)

400(0.15) + x(1) = (400+x)(0.32)

Simplify and solve for x.

60 + x = 128 + 0.32x

60 + 0.68x = 128

0.68x = 68

x = 100 ml of pure alcohol is require