
Shortcut Trick
Total work = LCM(10, 20, 40) = 40 units.
Daily efficiency: A = 4, B = 2, C = 1.
Work in one 3-day cycle = A + A + (A + B + C) = 4 + 4 + 7 = 15 units.
Work done in 6 days (2 cycles) = 30 units, leaving 10 units of remaining work.
Next 2 days, A completes 8 units (4 × 2). The remaining 2 units are done by A, B, and C in 2/7 days.
∴ The correct answer is 8 2/7 days.

Alternate Method
Given:
Time taken by A = 10 days
Time taken by B = 20 days
Time taken by C = 40 days
Formula Used:
Total Work = LCM of given days
Efficiency = Total Work ÷ Days
| Person | Days | Total Work | Efficiency |
|---|
| A | 10 | 40 | 4 |
| B | 20 | 2 | |
| C | 40 | 1 | |
Calculations:
⇒ Work done on Day 1 (by A) = 4 units
⇒ Work done on Day 2 (by A) = 4 units
⇒ Work done on Day 3 (by A + B + C) = 4 + 2 + 1 = 7 units
⇒ Work done in one complete 3-day cycle = 4 + 4 + 7 = 15 units
⇒ Number of full cycles = 40 ÷ 15 = 2 cycles (with remainder)
⇒ Work done in 2 cycles (6 days) = 15 × 2 = 30 units
⇒ Remaining work = 40 − 30 = 10 units
⇒ On Day 7, A completes 4 units → Remaining work = 6 units
⇒ On Day 8, A completes 4 units → Remaining work = 2 units
⇒ On Day 9, A, B, and C work together with a combined efficiency of 7 units/day
⇒ Time taken to complete the last 2 units = 2 ÷ 7 days
⇒ Total time taken = 6 + 1 + 1 + 2/7 = 8 2/7 days
∴ The correct answer is 8 2/7 days.

Additional Information
LCM Method for Time & Work
Total work is assumed as the Least Common Multiple (LCM) of the time taken by each individual. This guarantees that calculating efficiency always results in simple integer values.
Alternate Day Work Concept
When workers operate in a repeated pattern, first calculate the combined work done in one complete cycle. Multiply the cycle length to get as close to the total work as possible before resolving the final days individually.
Work & Wages
Wages are strictly distributed in proportion to the total physical work completed by each person. If all members work for the same total duration, wages are simply split in the ratio of their efficiencies.