Answer:
30 min
Step-by-step explanation:
The tank can be filled in 15 min, this means that in one min, 1/15 of the tank can be filled.
The tank can be emptied in 10 min, this means that in one min, 1/10 of the tank can be emptied.
the outflow rate - the inflow rate = rate of emptying the tank
1/10 - 1/15 = 1/x
where x is the time it will take to empty the tank
solving, we'll have
1/30 = 1/x
the reciprocal of the equation gives
x = 30 min
