Thread: Algebra word problem

A chemist ran out of a 72 ml solution of 12% alcohol. All that is left in the lab is 8% alcohol and 20% alcohol. How many ml of 8% and 20% would be needed to make a 72 ml solution of 12%?

This is what I have so far.

.12 X 72=8.64

.08x + .2y=8.64

(100) .08x + .2y=8.64 (100)

8x + 20y= 864


Any help in solving it would be appreciated. I am at a dead end.

Shouldn't x and y be equal to 72 ?

you can then make 2 equation, the one that you did
and x+y = 72
and solve them..

Do you mean x + y =72

The whole point is to find a solution using 8% and 20% alcohol.

You are probably a lot better at this than I am.
How could I set that up?

You have 2 unknowns and 2 equations..
x+y =72
2x+ 5y =216

solve them and find x and y

((you chose x to be the volume of the 8% solution
and y for the 20% solution))

let x= ml of 20% alc to be added to (72-x ) ml of 8% alc to make 72 ml of 12%alc
write an alc balance
0.2 x +(72-x)*0.08 = 0.12*72
x=24 72-x = 48