Question

Left on together, the cold and hot water faucets of a certain bathtub take 8 minutes to fill the tub. If it takes the cold water faucet 18 minutes to fill the tub by itself, how long will it take the hot water faucet to fill the tub on its own

Answer 1

cf=cold faucet rate
hf=hot faucet rate

cf*18min=1 tub
(cf+hf)*8min=1 tub
cf+hf=1tub/8min
cf=1tub/18min
hf=(1/8-1/18)tubs per minute
hf=5/72

It takes 14.4 minutes.