Question

A man can do a piece of work in 5 days, but with the help of his son he can do it in 3 days. In what time can the son do it alone?
1. 7.5 days
2. 8 days
3. 7 days
4. 6 days

Answer 1

Correct Answer - Option 1 : 7.5 days

Given:

A man can do a piece of work in 5 days.

With the help of his son he can do it in 3 days

Concept used:

Work = time × efficiency

Calculation:

work	time	efficiency
Man	5 days	15/5 = 3
Man + son	3 days	15/3 = 5
Total work (LCM)	15 units

Efficiency of son = efficiency of Man + son - efficiency of man

Efficiency of son = 5 - 3 = 2

∴ Time taken by son to finish work = 15/2 = 7.5 days.