A and B can together finish a work $30$ days. They worked together for $20$ days and then B left. After another $20$ days, A finished the remaining work. In how many days A alone can finish the work?

A, B and C can do a piece of work in $20,30$ and $60$ days respectively. In how many days can A do the work if he is assisted by B and C on every third day?

$A$ alone can do a piece of work in $6 \mathrm{days}$ and $B$alone in $8 \mathrm{days}$. $A$ and $B$ undertook to do it for $₹3200$. With the help of $C$, they completed the work in $3 \mathrm{days}$. How much is to be paid to $C$?

Two pipes $\mathrm{A}$ and $\mathrm{B}$ can fill a tank in $15$ minutes and $20$ minutes respectively. Both the pipes are opened together. But, after $4$ minutes, pipe $\mathrm{A}$ is turned off. What is the total time required to fill the tank?

A person crosses a $600$ m long street in $5$ min. What is his speed in km per hour?