P is thrice as good a workman as Q and therefore able to finish a job in 48 days less than Q. Working together, they can do it in?

Answer: A. 18 days

Since P is thrice as efficient as Q, P takes 1/3 of the time that Q takes to finish the job.
The Difference: The difference in their time is 2 units ( 3 - 1 ). The problem says that difference is actually 48 days. If 2 units = 48 days, then 1 unit = 24 days.. P takes 24 days and Q takes 72 days (3 units).
Together, their combined daily work rate is 1/24+ 1/72 = 4/72 , which simplifies to 1/18 of the job per day.
Therefore, working as a team, they will complete the entire job in 18 days.

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