Question 1207781
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Most of the responses you have received show some form of the standard algebraic solution, using the fact that the two faucets together fill 1/15 of the tub in 1 minute and the drain empties 1/20 of the tub in 1 minute.<br>
Here is a solution by an alternative method for solving this kind of "working together" problem.<br>
Consider the least common multiple of the two given times: the LCM of 15 and 20 is 60.<br>
In 60 minutes, the two faucets could fill the tub 60/15 = 4 times; in 60 minutes, the drain could empty the tub 60/20 = 3 times.<br>
So in 60 minutes the two faucets and the drain together could fill the tub 4-3 = 1 time.<br>
ANSWER: 60 minutes<br>