Tom has a 500 gallon pool. He is able to drain it at a rate of 15 gallons per minute. if the pool still has 170 gallons of water remaining, how many minutes was the pool draining?

( 500 -170 gal) / 15 gal/min = ............ mins

500-170 is equal to 330, so 330 gallons escaped. 330/15 is equal to 22, so 22 minutes had passed since the plug was pulled.