Work done by P in one day is double the work done by Q in one day and work done by Q in one day is thrice the work done by R in one day. If P, Q and R together can complete the work in 30 days then in how many days P alone can do the work?

It is given that work done by Q in one day is thrice the work done by R in one day.

Let us assume R completes K units of work per day.

Thus, Q will complete 3K units of work per day.

It is also given that the work done by P in one day is double the work done by Q in one day.

Therefore, P will complete 6K units of work per day.

Together, P, Q and R complete the total work in one day = 6K+3K+K = 10K units per day

They complete the work in 30 days.

So, total work done by them in 30 days = 30*10K = 300K units

If P works alone, he will complete 6K units daily.

So, the number of days taken by P alone to complete the work = 300K/6K = 50 days.