If 10 persons can do a job in 20 days then 20 persons with twice efficiency can do the same job in:

by

A. 10 days
B. 5 days
C. 3 days
D. None of these

🧠 Explanation (Math):

Given: 10 persons in 20 days; now 20 persons with twice efficiency
Step 1: Work $=10times20=200$ person-days.
Step 2: Effective persons $=20times2=40$.
Step 3: Time $=200/40=5$ days.
Final Answer: 5 days