Harish and Bimal can complete a task in 20 days. They worked at it for 15 days and then Bimal left. The remaining work was done by Harish alone, in 10 days. Harish alone can complete the entire task in:
- AOption (a)
40 days
- BOption (b)
30 days
- COption (c)
35 days
- DOption (d)
45 days
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Correct answer
40 days
Why this answer is correct
Shortcut Trick
Remaining days of work for Harish + Bimal = 20 − 15 = 5 days.
Work done by Harish alone in 10 days = Work done by (Harish + Bimal) in 5 days.
Efficiency Ratio (Harish + Bimal) : Harish = 10 : 5 = 2 : 1.
Since Harish's efficiency is half of their combined efficiency, he takes double the time.
Time taken by Harish alone = 20 × 2 = 40 days.
∴ The correct answer is 40 days.
Alternate Method
| Person | Days | Total Work | Efficiency |
|---|---|---|---|
| Harish + Bimal | 20 | 20 units | 1 unit/day |
Given: Harish and Bimal work together for 15 days.
⇒ Work completed in 15 days = 15 × 1 = 15 units.
⇒ Remaining work = 20 − 15 = 5 units.
⇒ Harish completes 5 units in 10 days.
⇒ Harish's efficiency = 5 ÷ 10 = 0.5 units/day.
⇒ Time for Harish alone = Total Work ÷ Efficiency
⇒ Time = 20 ÷ 0.5 = 40 days.
∴ The correct answer is 40 days.
Additional Information
Work and Efficiency Relation
Total Work = Efficiency × Time. Efficiency is inversely proportional to the time taken to complete a task.
Combined Efficiency
If person A takes x days and B takes y days, combined efficiency = (1/x + 1/y). Combined time = (x × y) ÷ (x + y).
Remaining Work Concept
Remaining work = 1 − (Work done). This is often used when a person leaves a task mid-way.





