If it takes chis 30 minutes to fill the pool and Sarah 45 minutes to fill the pool and Billy 90 minutes to fill the pool how long will it take all 3 to fill the pool?

Answer 1

chis fills (1/30) of the pool every minute.

Sarah fills (1/45) of the pool every minute.

Billy fills (1/90) of the pool every minute.

Working together, they fill [ (1/30) + (1/45) + (1/90) ] every minute.

(1/30) + (1/45) + (1/90) = (3/90) + (2/90) + (1/90) = (6/90) = 1/15

Together, they fill (1/15th) every minute, so it takes 15 minutes to fill it completely.