Question

See clear window cleaner is 40% vinegar and spot free window cleaner is 90% vinegar. How much of each should be used to make a 250 oz of a cleaner that is 60% vinegar?

Answer 1

okay so I would say to do
x = clear window cleaner and y = spot free window cleaner

x+y = 250
.4x+.9y=(.6)250 so .4x+.9y=150

We are going to use the substitution technique here so x=250-y from the top equation. Substitute that into the bottom

.4(250-y)+.9y=150 so now 100-.4y+.9y=150. 0.9-.4=.5 and 150-100 = 50
therefore
.5y=50
Divide by .5 and get 100 = y, substitute that back into x=250-y and get
x=250-100, so x =150.

Final answers: 

150 ounces of clear window cleaner and 100 ounces of spot free window cleaner