Time for filling and emptying tanks

Question

There are 10 tanks. It takes exactly 7 minutes to fill each tank, and the tanks must be filled one by one only. All the ten tanks can be emptied in 20 minutes. At the start, with all tanks filled, with the above conditions, how many tanks will be emptied in 24 hours?

Answer 1

20 minutes to empty 10 tanks and 70 minutes to fill them back up again

20+70=90 minutes

90 minutes=1.5 hours

24/1.5=16

the 10 tanks can be emptied and filled 16 times in 24 hours

16*10=160 tanks will be emptied in 24 hours