4 girls can do a piece of work in 8 days, 3 boys can do the same work in 9 days , 7 men can do the same piece of work in 2 days, 5 women can do a piece of work in 4 days. Who is least efficient?

Calculate work rate per person per day: Girls: 4 girls in 8 days = 32 girl-days for full work, so 1 girl does 1/32 per day. Boys: 3 boys in 9 days = 27 boy-days, so 1 boy does 1/27 per day. Men: 7 men in 2 days = 14 man-days, so 1 man does 1/14 per day. Women: 5 women in 4 days = 20 woman-days, so 1 woman does 1/20 per day. Least efficient = lowest rate = 1/32 (girls). Efficiency is inversely proportional to person-days needed.