A, B and C can individually complete a task in 24 days, 20 days and 18 days, respectively. B and C start the task, and they work for 6 days and leave. The number of days required by A alone to finish the remaining task is:

A, B and C can do one-third of a work in 15 days, 30 days and 10 days, respectively. A started the work. C joined him after 1 day and B joined them after 3 days of the beginning. For how many days did C work?

Pipe A and Pipe B can alone fill a tank in 20 hours and 30 hours, respectively and Pipe C alone can empty the tank in 15 hours. If pipe A opened alone for the first hour and Pipe B opened alone for the second hour and after the second hour all three pipes are opened, then the total time required to fill the tank is –