Let x be the volume of fluid removed and the volume of pure antifreeze that is added. The concentration of antifreeze in the fluid is 0.3, the concentration in pure antifreeze is 1 and that in the final solution is 0.4 The volume of the final solution is 10.
(10 - x)(0.3) + x = 10(0.4)
0.3 + 0.7x = 0.4
x = 1/7 quarts
The volume that should be drained is 1/7 quarts
