P, Q and R can complete a piece of work in 9, 12 and 18 days, respectively. Working together, how much work can they complete in one day?

Ram and Ramesh can do a work in 12 days, Ramesh and Somesh in 15 days and Somesh and Ram in 10 days. If Ram, Ramesh and Somesh work together, in how many days will they complete 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 both B and C on every third day?

Benny can do a piece of work in 24 days. Chethan and David can do the same work individually in 36 and 48 days, respectively. All of them begin the work together. However, Benny leaves the work 4 days before the completion of work and Chethan leaves the work 10 days before the completion of the work. David worked till the end and completed the work. Find the number of days in which the work was completed.