Reviewed by Aditya Kumar · Last reviewed 2026-03-24
**Formula**: Combined rate = 1/a + 1/b; time = 1/(1/a + 1/b). **Example**: A in 10 days, B in 15. Rates 1/10, 1/15. Together: 1/10 + 1/15 = 5/30 = 1/6. Time = 6 days. **Three workers**: 1/(1/a + 1/b + 1/c). **Pipes**: Fill positive, drain negative....
Pro-Move: Show your work step-by-step; write down rates before calculating. Red Flag: Guessing or skipping stepsâinterviewers want to see reasoning.
Formula: Combined rate = 1/a + 1/b; time = 1/(1/a + 1/b). Example: A in 10 days, B in 15. Rates 1/10, 1/15. Together: 1/10 + 1/15 = 5/30 = 1/6. Time = 6 days. Three workers: 1/(1/a + 1/b + 1/c). Pipes: Fill positive, drain negative. Best practice: Identify rates; add; invert for time.
Pro-Move: Show your work step-by-step; write down rates before calculating. Red Flag: Guessing or skipping stepsâinterviewers want to see reasoning.
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