John can do a piece of work alone in 20 days, while Ravi can do the same piece of work alone in 28 days. In how many days can the duo complete the same work if they work together?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. .
Concept used:
Work done = Efficiency × time
Calculations:
Let the total work done by John and Ravi (LCM of 20 and 28) = 140 units
Efficiency of John = 140/20 = 7 units
Efficiency of Ravi = 140/28 = 5 units
Required time = Total work done/(efficiency of john + efficiency of ravi)
⇒ 140/12 = days