Question

You need a 20% alcohol solution. on hand, you have a 240 ml of a 15% alcohol mixture. you also have 40% alcohol mixture. how much of the 40% mixture will you need to add to obtain the desired solution?

Answer 1

0.15*240=36 ml of alcohol in 240 ml of a 15% alcohol mixture
0.4x = ml of alcohol in x ml of a 40% alcohol mixture
0.2(x+240)= ml of alcohol in (x+240) ml of a 20% alcohol mixture

0.15*240 + 0.4x = 0.2(x+240)
36+0.4x=0.2x+48
0.2x = 12
x=12/0.2=120/6=20 ml  of a 40% alcohol mixture