18 men working 12 hr/days complete the work in 20 days, 24 women working 10 hr/day completes the same work in 15 days. 12 men and 15 women working together 8 hrs/day will complete the whole work in how many days?

Calculate total work: 18 men × 12 hr/day × 20 days = 4320 man-hours. 24 women × 10 hr/day × 15 days = 3600 woman-hours. Equating: 4320 man-hours = 3600 woman-hours, so 1 man-hour = (3600/4320) woman-hours = 5/6 woman-hour. Alternatively: 1 woman-hour = 6/5 man-hours = 1.2 man-hours. Combined daily work in man-hours: (12 × 8) + (15 × 8 × 6/5) = 96 + 144 = 240 man-hours/day. Days needed: 4320 ÷ 240 = 18 days.