Question

When only the cold faucet is fully turned on, a bathtub fills in 8 minutes. When only the hot faucet is turned on, the same bathtub fiills in 12 minutes. If both the cold and hot faucet are fully turned on, how long will it take to fill the bathtub?

Answer 1

rate of cold tap = bathtub/8
rate of hot = bathtub/12
combined rate = btb/8 + btb/12 = 5 btb/12

time at combined rate = btb/(5btb/12)
= btb(12/(5btb)) = 12/5 minutes or 4.8 minutes