Solution to puzzle 19

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The question was

The cold tap in my bath lets the water in at the rate of 15 litres per minute. The hot tap fills the bath at the rate of 10 liters per minute. The plug hole lets the water out of the bath at the rate of 12 liters per minute.
The bath holds a maximum of 520 liters. I turn both taps on, but forget to put the plug in.
How many minutes does it take for the bath to overflow?


Solution :  40 minutes

If both the taps are turned on, water inlet to the bath is
      15+10 = 25 liters per minute
The water going out of plughole = 12 liters per minute

So per minute the water getting added to bath is 25-12 = 13 liters

The time taken to fill the bath will be 520/13 = 40 minutes

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