3 pipes at a time 2
A tap can fill a bath in 20 minutes and another in 30 minutes. Calvin opens both the taps simultaneously. By the time the bath should have been full, He finds that the waste pipe was open. He then closes the waste pipe and the bath is filled up in 4 minutes. In what time can the waste pipe empty the bath? (in minutes)
The answer is 36.
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1 solution
Fraction of the bath filled by both the taps in 1 minute= 1 2 1 + 3 0 1 = 1 2 1
The waste pipe can empty as much of the bath in 12 minutes that the two taps can fill in 4 minutes
The taps can fill the bath tub in 12 minutes, therefore they can fill 3 1 of the tank in 4 minutes.
Hence, This implies, The waste pipe can empty 3 1 of the bath in 12 minutes
Therefore it can empty the complete tank in 1 2 × 3 = 3 6 minutes.