SOLUTION: There are two small valves in the bottom of a tub filled with water. If opened, one valve will empty the tub in three hours; the other will empty it in six hours. If both valves

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Question 214842: There are two small valves in the bottom of a tub filled with water. If opened, one valve will empty the tub in three hours; the other will empty it in six hours. If both valves are opened at the same time, how long will it take to empty the tub?
Answer by Alan3354(69443) About Me  (Show Source):
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There are two small valves in the bottom of a tub filled with water. If opened, one valve will empty the tub in three hours; the other will empty it in six hours. If both valves are opened at the same time, how long will it take to empty the tub?
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The small one empties 1/6 of the tub per hour.
The other one 1/3 per hour.
Add them
1/6 + 1/3 = 3/6 = 1/2 tub per hour.
--> 2 hours.
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A shortcut: product/sum
3*6/(3+6) = 18/9
= 2 hours