In a day 2 men do as much work as 3 women, and 3 women do as much as 5 children. If 4 men, 6 women and 10 children together finish a job in 8 days, how many days will 6 men alone take to finish the same job?

Value a child's day at 1 unit. Then 3 women = 5 children, so a woman is 5/3 units; and 2 men = 3 women = 5 children, so a man is 2.5 units. The mixed crew gives $4(2.5)+6(5/3)+10(1)=10+10+10=30$ units a day, so the job is $30\times 8=240$ units. Six men give 15 units a day: 240 ÷ 15 = 16 days. 24 days keeps the crew's four men (240 ÷ 10) instead of the six asked about. 20 days values a man at only 2 children. 40 days values a man at a single child-unit while still using the 240-unit job size.