In what time would a cistern be filled by three pipes whose diameters are $1 \text{ cm}$,$1 \frac{1}{3} \text{ cm}$,and $2 \text{ cm}$,running together,when the largest alone will fill it in $61 \text{ minutes}$,the amount of water flowing in by each pipe being proportional to the square of its diameter? (in $\text{minutes}$)

If a pipe fills a tank in $6 \ h$,then what part of the tank will the pipe fill in $1 \ h$?

Three taps $A, B$ and $C$ can fill a tank in $12, 15$ and $20$ hours respectively. If $A$ is kept open all the time,and $B$ and $C$ are opened for one hour each alternately,how long will it take to fill the tank?

$A$ water tank has three taps $A, B, C$. Tap $A$,when opened,can fill the water tank alone in $4$ hours. Tap $B$,when opened,can fill the water tank alone in $6$ hours,and tap $C$,when opened,can empty the water tank alone in $3$ hours. If taps $A, B,$ and $C$ are opened simultaneously,how long (in hours) will it take to fill the tank completely?

If three taps are opened together,a tank is filled in $12$ $hrs$. One of the taps can fill it in $10$ $hrs$ and another in $15$ $hrs$. How many $hours$ does the third tap take alone to empty it completely?

Two pipes $A$ and $B$ can fill a cistern in $20$ $minutes$ and $25$ $minutes$ respectively. Both are opened together,but after $5$ $minutes,$ $B$ is turned off. How much time (in $minutes$) longer will the cistern take to fill?