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Two pipes can fill a tank in 12 and 15 minutes respectively and a waste pipe can empty 3.4 litres per minute. All the three pipes working together can fill the tank in 18 minutes. The capacity of the tank is

Solution

✅ Correct Option: 3

Combined rate of the filling pipes =112+115=320= \dfrac{1}{12}+\dfrac{1}{15} = \dfrac{3}{20} tank per minute.

With the waste pipe, the net rate is 118\dfrac{1}{18}, so the waste pipe empties 320−118=17180\dfrac{3}{20}-\dfrac{1}{18} = \dfrac{17}{180} of the tank per minute.

Since that equals 3.4 litres, capacity =3.4×18017=36= 3.4\times\dfrac{180}{17} = 36 litres.

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