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1. Two pipes can fill a tank in 40 and 48 minutes respectively and a waste pipe can empty 3 gallons per minutes. All the three pipes working together can fill the tank in 30 minutes, The capacity of the tank is-

A. 60 gallons

B. 120 gallons

C. 180 gallons

D. 240 gallons

Solution:

Work done by the waste pipe in 1 minute

\begin{aligned} = \frac{1}{30} - (\frac{1}{40} + \frac{1}{48}) \\ = (\frac{1}{30} - \frac{11}{220}) \\ = - \frac{1}{80} [- Nagetive sign means emptying] \\ ∴ Volume of \frac{1}{80} part  =  3 galons \\ Volume of whole tank \\ = (3 \times 80) gallons \\ =  240 gallons \end{aligned}

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