Question 395193
a pool can be filled water using pipe a in 4hrs drained using pipe b in 10 hours. if pipe b is accidentally left open while the pool is being filled how, long will it take to fill the pool

pipe A ----- 4 hours
so it does 1/4 of job in 1 hour,
Pipe B ----------- 10 hours
so it does 1/10 of the job in 1 hour.
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1/4 -1/10 is the job done in 1 hour when both are open
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(10-4)/40= 6/40 = 3/20 of the job 
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so it will take 20/3 hours to fill the pool.
=6.66 hours