A swimming pool can be filled in 15 hours if water enters through a pipe alone, or in 23 hours if water enters through a hose alone. If water is entering through both the pipe and the hose, how long will it take to fill the pool?

9.08 hours

Step-by-step explanation:

in order to fill 1 pool

fill rate by pipe = 1 pool / 15 hours = 1/15 pool per hour

fill rate by hose = 1 pool / 23 hours = 1/23 pool per hour

combined rate = fill rate by pipe + fill rate by pool

= 1/15 + 1/23 = 38/345 pool per hour

since:

38/345 pool >  will take 1 hour

1 pool > will take 1 hour x (345/38) = 9.08 hours

9.08 hours

Step-by-step explanation:

(23×15)/(23+15)

345/38

9.08 hours

answer: 21$

step-by-step explanation:

$42 / $14 = 3   (ratio 3: 1)

$7 x 3 = $21