How much of a 40% antifreeze solution must a mechanic mix with an 80% antifreeze solution if 20 gallons of a 50% antifreeze solution are needed.

Question

Problem solving using system of two equations

Answer 1

a + b = 20 (we need 20 gallons total)

.4a + .8b = .5(20)

 

Since we only need to know what a is, we are going to solve the first equation for b. You'll see why.

 

b = 20 - a

 

Now, we substitute our "value" for b into the 2nd equation.

 

.4a + .8(20 - a) = .5(20)

 

I bet you can solve for a and get your answer!