You paint 1/2 wall in 1/4 hour. at that rate, how long will it take you to paint one wall?

(1/2) / (1/4) = 1 / x1/2 wall to 1/4 hr = 1 whole wall to x hrs
cross multiply
(1/2)(x) = (1/4)(1)
1/2x = 1/4
x = 1/4 * 2
x = 2/4 reduces to 1/2so it will take 1/2 hr (or 30 minutes) to paint the whole wall.