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CSS Paper: General Science 2019 Q.6(b)
One pipe can fill a pool 1.25 times as fast as a second pipe. When both pipes are opened they fill the pool in five hours. How long would it take to fill the pool if only the slower pipe is used?

Solution

Let pipe-1 (which is slower) fills the pool in x hours, then pipe-2 (which is 1.25 times faster) can fill the pool in 1.25x hours. Together they can fill the pool in 5 hours. Therefore,

Hence, pipe-1 (the slower pipe) can fill the pool in 9 hours. Answer.