Panu, Jiban, and Jalil can complete a certain task individually in 30, 20 and 60 days, respectively. Jiban started work on the task and Panu and Jalil agreed to help Jiban every third day. How many days will it take to complete the task?
- AOption (a)
13
- BOption (b)
12
- COption (c)
14
- DOption (d)
15
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Correct answer
15
Why this answer is correct
Shortcut Trick
Let Total Work be 60 units (LCM of 30, 20, 60).
Efficiencies: Panu = 2, Jiban = 3, Jalil = 1.
Work in 3 days: Jiban (Day 1) + Jiban (Day 2) + All three (Day 3) = 3 + 3 + (2+3+1) = 12 units.
To finish 60 units: (60 ÷ 12) × 3 days = 15 days.
∴ The correct answer is 15 days.
Alternate Method
Given: Individual days for Panu = 30, Jiban = 20, Jalil = 60.
| Person | Days | Total Work | Efficiency |
|---|---|---|---|
| Panu | 30 | 60 | 2 |
| Jiban | 20 | 3 | |
| Jalil | 60 | 1 |
Calculations:
⇒ Work done on Day 1 (Jiban) = 3 units
⇒ Work done on Day 2 (Jiban) = 3 units
⇒ Work done on Day 3 (Jiban + Panu + Jalil) = 3 + 2 + 1 = 6 units
⇒ Total work done in a 3-day cycle = 3 + 3 + 6 = 12 units
⇒ Number of cycles required = 60 ÷ 12 = 5 cycles
⇒ Total days = 5 × 3 = 15 days
∴ The correct answer is 15 days.
Additional Information
Total Work Concept
Total work is always considered as the Least Common Multiple (LCM) of the individual days to avoid fractions during calculation.
Efficiency Relationship
Efficiency is inversely proportional to the time taken. Efficiency = Total Work ÷ Time.
Alternate Day Work
In problems involving assistance or alternate days, calculate the work done in one complete cycle and then multiply to reach the target work.























