SOLUTION: If A can Fill tank in 20 min and B can empty that tank in 30 min, If they work alternatively 1 min, then how much time has been taken to filled the tank completely.

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Question 896278: If A can Fill tank in 20 min and B can empty that tank in 30 min, If they work alternatively 1 min, then how much time has been taken to filled the tank completely.
Answer by josgarithmetic(39799) About Me  (Show Source):
You can put this solution on YOUR website!
A and B alternate over a 2 minute period for some quantity of these periods.

%281%2F20%29%2A1-%281%2F30%29%2A1, a two minute period.
Same as (1/20-1/30)*p, using p to count the number of these two-minute periods.

Fill 1 tank.
%281%2F20-1%2F30%29p=1
%283%2F60-2%2F60%29p=1
%281%2F60%29p=1
p=60, the count of the two-minute alternating time periods.

This means, 2%2Ap=2%2A60=120 minutes,
2 hours.