A contractor decided to complete a work in 80 days and employed 60 men at the beginning and 20 men additionally after 20 days and got the work completed as per schedule. If he had not employed the additional men, how many extra days would he have needed to complete the work (round off to the nearest integer)?

Work = 60 × 20 + 80 × 60 = 4800 man-days. Without additional men: 60 × 80 would complete 4800 man-days, but we need to find when 60 men complete 4800 - 1600 = 3200 man-days. Time = 3200/60 = 53.33 days. Total would be 20 + 53.33 ≈ 73.33 days. Extra days = 73.33 - 80 = 6.67, but we need 80 - 60 = 20 more days total. Actually: 60 men in 100 days complete 4800. So extra = 100 - 80 = 20 days.