15 pipes, each having the same diameter, can fill a cistern in 12 minutes. How long will it
take for 6 pipes, each with double the original diameter,to fill the same cistern at the same speed of the flow?
Let the time taken by one pipe to fill the tank be x.
So , $$\frac{15}{x} = \frac{1}{12}$$
$$\frac{1}{x} = \frac{1}{12 \times 15}$$
Work of 6 pipes with double diameter would be
$$\frac{6 \times 4}{12 \times 15}$$Â
=$$\frac{1}{7.5}$$
So , 6 pipes with double diameter can fill the tank in 7.5 minutes.
So , the answer would be option d)7.5 minutes.
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