A bathtub has separate taps for hot and cold water. With the cold water tap you can fill the tub in 6 minutes and 40 seconds. With the hot water tap it takes exactly 8 minutes. If the tub is full and you pull out the stopper it takes 13 minutes and 20 seconds for the tub to drain.
If you leave the stopper out and open both the hot and cold water taps how long will it take to fill the tub?
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