According to the question, Let efficiency of each person is 1. Total work =20 unit On first day 1 unit done, 2 nd day =2 unit, 3rd day =3 unit, 4th day =4 unit, 5th day =5 unit Total work completed =1+2+3+4+5 =15 unit Remaining work to complete =20−15=5 unit After that next day all 5 person jointly work 5 unit. So, total 6 days will required to complete a work.