Question:
A can complete a task in 15 days, B in 20 days. Together, how many days?
A can complete a task in 15 days, B in 20 days. Together, how many days?
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Add work rates or use LCM to find combined rate for time and work problems.
Updated On: Jul 31, 2025
- 8.57 days
- 9 days
- 10 days
- 12 days
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The Correct Option is A
Solution and Explanation
- Step 1: Work rates. A: $\frac{1}{15}$ task/day. B: $\frac{1}{20}$ task/day.
- Step 2: Combined rate. $\frac{1}{15} + \frac{1}{20} = \frac{4 + 3}{60} = \frac{7}{60}$.
- Step 3: Time. Time = $\frac{1}{\frac{7}{60}} = \frac{60}{7} \approx 8.57$ days.
- Step 4: Alternative. LCM(15, 20) = 60 units. A: $\frac{60}{15} = 4$ units/day. B: $\frac{60}{20} = 3$ units/day. Combined: $4 + 3 = 7$ units/day. Time = $\frac{60}{7} \approx 8.57$ days.
- Step 5: Conclusion. Option (1) 8.57 days is correct.
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