You can put this solution on YOUR website!
A water faucet can fill a sink in 6 minutes, whereas the drain can empty it in 4 minutes. If the sink is full, how long will it take to empty if both the faucet and drain are both open?
1/6=flow-rate of faucet
1/4=flow-rate of drain
x=minutes to empty sink when faucet and drain are both open
1/x=net flow rate when faucet and drain are both open
It would take 12 minutes to empty sink when faucet and drain are both open
The faucet would add water for 2 full sinks=1/6*12=2
The drain would take out water for 3 full sinks=1/4*12=3 (existing full sink plus 2 added by faucet)