Three taps $A, B$ and $C$ fill a tank in $20$ min,$15$ min and $12$ min,respectively. If all the taps are opened simultaneously,how long will they take to fill $40 \%$ of the tank (in $min$)?

Two pipes $A$ and $B$ can fill a water tank in $10$ and $12$ $min,$ respectively,and a third pipe $C$ can empty it at the rate of $6$ $gallons$ per $min.$ If $A, B,$ and $C$ are opened together,they fill the tank in $20$ $min.$ What is the capacity (in $gallons$) of the tank?

Three pipes $A, B$ and $C$ can fill a tank from empty to full in $30$ minutes,$20$ minutes and $10$ minutes respectively. When the tank is empty,all the three pipes are opened. $A, B$ and $C$ discharge chemical solutions $P, Q$ and $R$ respectively. What is the proportion of solution $R$ in the liquid in the tank after $3$ minutes?

Two pipes can fill a tank in $20$ $minutes$ and $24$ $minutes$ respectively,and a waste pipe can empty $3$ $gallons$ per minute. All the three pipes working together can fill the tank in $15$ $minutes$. The capacity of the tank is (in $gallons$):

Two inlet pipes can fill a cistern in $10$ $hours$ and $12$ $hours$ respectively,and an outlet pipe can empty $80$ $gallons$ of water per hour. All three pipes working together can fill the empty cistern in $20$ $hours$. What is the capacity (in $gallons$) of the tank?

$A$ tank is filled in $5$ $hours$ by three pipes $A, B$ and $C$. Pipe $C$ is twice as fast as $B,$ and $B$ is twice as fast as $A$. How much time (in $hours$) will pipe $A$ alone take to fill the tank?