Question 1045345
A+B+C=1/1 of tank per hour
A+C=1/1.5 of tank per hour or 2/3
-A=C=-2/3
B=1-2/3=1/3 tank alone per hour
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A+B+C=1
-B-C=-1/2
A=1/2 tank alone per hour
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C=1/6 tank alone per hour , since they all add to 1.
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With A and B open, 5/6 of the tank is filled per hour.
That will require 6/5 hours or 72 minutes to fill with these two valves.