A and B, working 8 hours a day, can do a piece of work in 20 days and 30 days, respectively. On weekends, they work for only 1 hour and on weekdays, they work for 4 hours. If they start working together on Sunday, then on which day will they finish the task? (Assume that weekend includes Saturday and Sunday)

A works 4h/day weekdays, 1h/day weekends. Total work 8h/day for 20 days = 160h. A's rate = 1/160 per hour. B's rate = 1/240 per hour. Combined rate = 1/160 + 1/240 = 5/480 = 1/96 per hour. They work 4h/day weekdays and 1h/day weekends. Weekly work = 5*4 + 2*1 = 22 hours. Total work needed = 96 hours. 4 weeks = 88 hours. Remaining 8 hours finished on Tuesday.