3 men and 7 women can complete a piece of work in 12 days. 7 men and 3 women can complete the same work in 8 days. In how many days can 3 women complete the work alone?

Let m = work done by 1 man in 1 day, w = work done by 1 woman in 1 day. From first equation: 3m + 7w = 1/12 (work per day). From second: 7m + 3w = 1/8. Solving: Multiply first by 7: 21m + 49w = 7/12. Multiply second by 3: 21m + 9w = 3/8. Subtract: 40w = 7/12 - 3/8 = 14/24 - 9/24 = 5/24. So w = 5/960 = 1/192. Three women do 3w = 3/192 = 1/64 work per day, so they need 64 days.