Discussion

Question:

Two pipes can fill a cistern in 18 hrs and 24 hrs respectively. In how much time will they fill the cistern if both of them are opened together?

Explanation:

Work done by 1st pipe in 1 hour = 1/18

Work done by 2nd pipe in 1 hour = 1/24

∴ Work done by both pipes in 1 hour = $\frac{1}{8} + \frac{1}{24} = \frac{7}{72}$ 1/18+1/24)=7/72

∴ Both pipes together can fill in 72/7 hrs i.e., $10 \frac{2}{7}$ hours

Hence, option (c).

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