SOLUTION: One pipe can fill a pool in 9 hours and another pipe can fill the same pool in 12 hours. To fill up the pool, only the first pipe was turned on. After three hours it broke down, an

Question 783272: One pipe can fill a pool in 9 hours and another pipe can fill the same pool in 12 hours. To fill up the pool, only the first pipe was turned on. After three hours it broke down, and the second pipe was automatically turned on.
a) How many hours did it take to fill up the pool?
b) Hom many hours would it take to fill up the pool if the two pipes started to work together?
Found 2 solutions by mananth, MathTherapy:
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
One pipe can fill a pool in 9 hours and another pipe can fill the same pool in 12 hours. To fill up the pool, only the first pipe was turned on. After three hours it broke down, and the second pipe was automatically turned on.
a) How many hours did it take to fill up the pool?
b) Hom many hours would it take to fill up the pool if the two pipes started to work together?
pipe I does 1/9 of the job in 1hour
In 3 hours it does 3/9 =>1/3 of the job
Balance job = 1-1/3 = 2/3 of the job.

Pipe II does 1/12 of the job in 1 hour
to do 1/3 of the job it will take (1/3)/(1/12) = 4 hours
Total time = 3 + 4 = 7 hours
-----------------
Together they do 1/9 + 1/12 of the job in 1 hour
so they do 7/36 of the job in 1 hour
to complete the job they will take 36/7 hours
5.14 hours

Answer by MathTherapy(10552) (Show Source): You can put this solution on YOUR website!

One pipe can fill a pool in 9 hours and another pipe can fill the same pool in 12 hours. To fill up the pool, only the first pipe was turned on. After three hours it broke down, and the second pipe was automatically turned on.
a) How many hours did it take to fill up the pool?
b) Hom many hours would it take to fill up the pool if the two pipes started to work together?

a) It takes pipe one 3 hours to fill of pool

It takes pipe two 8 hours to fill remaining of pool

It takes 3 + 8, or hours to fill pool

b) With both turned on, it'll take , or hours to fill pool.

You can do the check!!

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