Two large and 1 small pumps can fill a swimming pool in 4 hours. one large and 3 small pumps can also fill the same swimming pool in 4 hours. how many hours will it take 4 large and 4 small pumps to fill the swimming pool.(we assume that all large pumps are similar and all small pumps are also similar.)

We can see through simple math that each large pump fill the pool at a rate equal to two small pumps, so we find how many small pumps it takes to fill the pool in 4 hours (5). Then find the equivalent number of small pumps in the final situation (12). I don't know how to explain it past that. It takes 1.6 hours.

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