Question
Pipe ‘A’ can fill a tank in 20 hours while pipe
‘B’ can empty it in 30 hours. They were operated on alternate hours starting with pipe ‘A’. Find the percentage of tank filled this way in 57 hours.Solution
Given: Pipe A fills in 20 hours → Rate = 1/20 Pipe B empties in 30 hours → Rate = 1/30 Net work in 2 hours = 
57 hours = 28 cycles + 1 hour.
Work in 28 cycles = 
Work by A in 1 hour = 1/20
Total filled = 
Percentage filled = 
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