A completes $\frac{7}{20}$ of a work in 10 days. Then he completes the remaining work with the help of B in 5 days. The time required for A and B together to complete the entire work is:

Rajan does $\frac{7}{11}$ of a work in 21 days. How many more days will he take to complete the work?

A and B working together can finish a piece of work in 12 days while B alone can finish the same work in 30 days. Then determine that in how many days can A alone finish the same work?

Rakesh can do a certain job in 12 days. Vipin is 60% more efficient than Rakesh. How many days will Vipin alone take to do the same job ?

X, Y and Z together can do a piece of work in 16 (4/11) days. X and Y together can do the same work in 20 days. In how many days will Z alone finish the 60% of the work?

If 36 persons can finish 50% of work in 12 days In how many days 72 person can finish the complete work?

P, Q and R can complete a work in 12, 9 and 15 days respectively. Working together, they will complete the same work in: