Answer:
Step-by-step explanation:
5 men × 15 days = 75 man-days
Each man does 1/75 of the job per day
7 women × 15 days = 105 woman-days
Each woman does 1/105 of the job per day.
9 girls × 15 days = 135 girl-days
Each girl does 1/135 of the job per day.
Least common multiple of 75, 105, and 135 =
Working together, 1 man, 1 woman, and 1 girl do 1/75 + 1/105 + 1/135 = 143/4725 of the job per day, finishing in 4725/143 = 33.04 days