Solution word problem.

Question

A 4% solution is mixed with 8 gallons of a 9% solution to produce a 6% solution. How many gallons of 4% solution was mixed? This is a fill in the blank answer. Gallons is assumed. 

Answer 1

Let x = the amount of 4% (0.04) solution that is mixed with 6 gallons of 9% (0.09) solution to get some quantity of 6% solution (0.06). 

We can set up our equation by multiplying the percentage of the solution to the volume:

0.04x + (0.09) (8) = (0.06)(x + 8)

simplify and solve for x:

0.04x + .72 = 0.06x + .48

.24 = 0.02x

x = 12 gallons