3 pipes take 12 hours ⇒ In 1 hour, the 3 pipes can fill 1/12 of the pool
2 of the pipes take 18 hours ⇒ in 1 hour, the 2 pipes can fill 1/18 of the pool
In 1 hour, the third pipe alone can fill :
Time needed :
---------------------------------------------------------------------------------------- Answer: It will take 36 hours for the third pipe to fill the pool. ----------------------------------------------------------------------------------------