A chemist needs 30mL of a 12% acid solution for an experiment. The lab has available a 10% solution and a 25% solution. How many milliliters of the 10% solution and how many milliliters of the 25% solution should the chemist mix to make the 12% solution?

parts of 10% soln, x

parts of 25% soln, y

total soln, x+y = 30

{x (0.1) + y (0.25) } / (x + y) = 0.12 ... eqn 1

x + y = 30 ... eqn 2

from eqn 2 ... = " x = 30-y

subst for x in eqn 1 ...

=" { (30-y) (0.1) + y (0.25) } / 30-y+y = 0.12

=" (3-.1y+.25y) / 30 = 0.12

=" 3+.15y = 3.6

=".15y =.6

=" y = 4

using x = 30 - y = 26

ans

26ml of 10% soln

4ml of 25% soln