Dr. W needs 1600 ml of 70%-ethanol solution. He has two solutions of ethanol. Solution A is 60% ethanol and Solution B is 75% ethanol. How much of Solution A and Solution B does he need to mix together in order to get 1600 ml of 70%-ethanol solution?

We need 1,600 ml of 70% ethanol.

x is ml of 60% and

y is ml of 75%

A) x + y = 1,600

B).60x +.75y =.70 * 1,600

Multiplying equation A by -.60

A) -.60 x -.60y = - 960 Then adding this to equation B

B).60x +.75y =.70 * 1,600

.15y = - 960 + 1,120

.15y = 160

y (75%) = 1,066.66 ml

x (60%) = 533.33 ml