Step-by-step solution:
- Let W be the efficiency of a woman and M be the efficiency of a man.
- We are given the relation: 3M=5W⟹M=35W.
- The total work can be calculated using the women's data:
Total Work=21W×20 days×10 hours/day=4200W units
- Now, we need to find the number of days (D) for 21 men working 8 hours a day to complete the same work.
- Work done by men = 21M×D×8
- Substitute M=35W:
21(35W)×D×8=4200W
- Simplify the equation:
35W×8×D=4200W
280D=4200
D=2804200=15
The 21 men will complete the work in 15 days.