Shortcut Trick
Total Work = LCM(10, 50) = 50 units.
Efficiency of (A + B) = 5 units/day and Efficiency of C = 1 unit/day.
Total Efficiency (A + B + C) = 5 + 1 = 6 units/day.
Given A = B + C, so Efficiency of A = 6 ÷ 2 = 3 units/day.
Efficiency of B = Efficiency of (A + B) − Efficiency of A = 5 − 3 = 2 units/day.
Time for B = 50 ÷ 2 = 25 days.
∴ The correct answer is 25 days.
Alternate Method
Given:
Time taken by (A + B) = 10 days
Time taken by C alone = 50 days
Condition: Efficiency of A = Efficiency of (B + C)
| Person | Days | Total Work | Efficiency |
|---|
| (A + B) | 10 | 50 units | 5 |
| C | 50 | 1 | |
Calculations:
⇒ Total efficiency of (A + B + C) = 5 + 1 = 6 units/day
⇒ Since Efficiency of A = Efficiency of (B + C)
⇒ A + (B + C) = 6 ⇒ A + A = 6
⇒ 2 × Efficiency of A = 6
⇒ Efficiency of A = 3 units/day
⇒ Efficiency of B = Efficiency of (A + B) − Efficiency of A
⇒ Efficiency of B = 5 − 3 = 2 units/day
⇒ Time taken by B alone = Total Work ÷ Efficiency of B
⇒ Time = 50 ÷ 2 = 25 days
∴ The correct answer is 25 days.
Additional Information
Work and Efficiency Relationship
Efficiency is inversely proportional to the time taken to complete a work. Efficiency = Work ÷ Time.
Combined Efficiency
When multiple people work together, their total efficiency is the sum of their individual efficiencies.
Time Calculation
Total time taken to complete the work = Total Units of Work ÷ Combined Efficiency.