A boy starts painting a fence, 2nd day 2 boys join him, 3rd day 3 more boys joined them and so on, fence is painted in 20 days. How many days will be taken by 10 men to paint the whole fence if efficiency of 1 man is equal to efficiency of 2 boys?
- A. 67
- B. 74
- C. 84
- D. 77 ✓
Correct Answer: D. 77
Explanation
Work sequence follows triangular numbers: 1 + 3 + 6 + 10 + \dots for 20 days. Total work = \frac{20 \times 21 \times 22}{6} = 1540 boy-days. Since 10 men = 20 boys, time taken = \frac{1540}{20} = 77 days.
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