Sanjay and Tannu working separately can do a piece of work in 6 and 20 days, respectively. If they work for an alternate day, Tannu beginning, in how many days will the work be completed?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 9.5.
Total work = LCM(6, 20) = 60 units
Sanjay’s efficiency = 60 ÷ 6 = 10 units/day
Tannu’s efficiency = 60 ÷ 20 = 3 units/day
Work in 2-day cycle (Tannu + Sanjay) = 3 + 10 = 13 units
After 4 cycles (8 days) → 4 × 13 = 52 units done
Remaining = 60 − 52 = 8 units
Day 9 (Tannu) does 3 units → remaining = 5 units
Day 10 (Sanjay) needs to do 5 units out of his 10 units/day → 5 ÷ 10 = 0.5 day
Total time = 8 + 1 + 0.5 = 9.5 days