suppose that we have two different sources of water. one is filling the tank full with 90 min and the other one is filling it up in 30 min. If we combined the two sources together, then how many minutes will take to fill the same tank ?
I found this question in a child book. I tries to solve it out and I found the most logical answer is 27,7 while 100/3=3.3 so 30-3.3=27.7
is this solution right ? others says it is 22,5 min. Can anyone relate?
Best Answer
The part filled by tap $A $ in one minute $=\frac{1}{90} $.
The part filled by tap $B $ in one minute $=\frac {1}{30}$.
The part filled by taps $(A+B) $ in one minute $=(\frac {1}{90}+\frac {1}{30}) =\frac {4}{90} = \frac {1}{22.5} $.
Thus both pipes can fill in $22.5$ minutes. Hope it helps.