Question

90% acid solution (90% pure acid and 10% water) and 97% acid solution are mixed to obtain 21 litres of 95% acid solution . how many litres of each solution are mixed?

Answer 1

If A is the volume (litres) of the first acid solution and B the volume (litres) of the second:

A+B=21. Therefore B=21-A.

The amount of acid in A is 0.9A L and that in B is 0.97B L, and the mixture is 0.95 L, so:

0.9A+0.97B=0.95×21=19.95.

0.9A+0.97(21-A)=19.95,

0.9A+20.37-0.97A=19.95,

20.37-19.95=(0.97-0.90)A,

0.42=0.07A, A=0.42/0.07=42/7=6L, making B=21-6=15L.

Therefore, we need 6L of the 90% acid solution and 15L of the 97% solution.