Ehsan can fill a pool carrying buckets to water in 30 minutes. Suman can do the same job in 45 minutes. Tonmoy can do the same job in 1(1/2) hours. How quickly can all three fill the pool together?

A 12 min

B 15 min

C 21 min

D 23min

Correct Answer: Option B

all three fill the pool together in 1 min = (1/30+1/45+1/91 ) =1/15 part

1/15 part filled in 1 min

1 part filled in 15 min