Together A and B can do the work in (1/20 + 1/30 = 5/60) = 12 days.B alone worked for 5 days i.e. B completed 5/30 = 1/6 th work.A and B worked together for 4 days i.e they completed 4/12 = 1/3 rd work.Total work left = 1 - (work completed by B) - (work completed by A and B) = 1 - 1/6 -1/3 = 1/2We know that A and B can work together for 12 days to finish the work.To complete 1/2 the work it will t