Question

Between 10 P.M. and 7:20 A.M.​, the water level in a swimming pool decreased by 4/15 . Assuming that the water level decreased at a constant​ rate, how much did the water level drop each​ hour?

Answer 1

1/35 every hour

Explanation:

The number of hours between 10pm and 7:20AM is 9 hours and 20 minutes. This is computed by noting that there are 2 hours till midnight and then 7 hours and 20 minutes till 7:20AM

So total time the water decreased = 9 hours and 20 minutes
20 minutes = 20/60 = 1/3 of an hour
So time taken in hours = 9 1/3 = 28/3 hours

4/15 of the pool depth decreased in 28/3 hours

Rate of decrease per hour = 4/15 ÷ 28/3

=4/15 x 3/28 =(4 x 3)/(15 x 28) = 12/420

Dividing numerator and denominator by 12 gives
(12 ÷ 12)/(420 ÷ 12) = 1/35

So the water level dropped by 1/35 every hour