Question 495049
a water tank can be filled in 8 minutes and emptied in 9 minutes.
 if the drain is accidentally left open when the tank is filled, how long does it take to fill the tank?
:
Let t = time in minutes empty the tank with both valves open
let an empty tank = 1
:
{{{t/8}}} - {{{t/9}}} = 1
multiply by 72 to clear the denominators, results:
9t - 8t = 72
t = 72 minutes