math
posted by asha on .
a local hardware store has a 10gallon can of gray paint left over that is a mixture of 35% black paint and 65% white paint. how many gallons of white paint will be needed to make the gray mixture 20% black?
note: answers must be 5 gallons, 7.5 gallons, 12 gallons, or 17.5 gallons.

Well, it it contains .35*10 gallons of black paint now, then
black paint =.20*total
.35*10=.20(10+w)
right? solve for w