Question

A chemist has two solutions of hydraulic acid. one is 50% and the other is 80%. How much of each should be used to obtain 100ml of 68% solution?

Answer 1

equation of total mass
x + y = 100
equation for hydrochloric acid 
0.5x + 0.8y = 0.68 x 100.
so,
x + y = 100
y = 100 - x  putting this eq in the other equation

0.80X+.50(100-X)=.68 x 100
0.80X+ 50- 0.50X=68
0.30X=68-50
0.30X=18
x=18/0.30

x =60 ml of 80% solution is used
100-60=40 ml of 50% solution is used