Three taps A, B and C can fill a cistern in 12, 15 and 18 minutes, respectively. They are all turned on, but after 4.5 minutes A and C are turned off. How many minutes longer will B take to fill the cistern?

Using the least common multiple method for 12, 15, and 18 gives a total cistern capacity of 180 units. The individual rates for taps A, B, and C are 15 units per minute, 12 units per minute, and 10 units per minute respectively. Working together for 4.5 minutes, the three taps fill 4.5 multiplied by 37, totaling 166.5 units and leaving 13.5 units to be filled. Tap B working alone at 12 units per minute will take 13.5 divided by 12, equaling 1.12 minutes to finish filling the cistern.

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