Vikas and Vishal can do a job in 7 days and 14 days respectively. They began the work together but 4 days before the completion of job, Vikas leaves the work. In how many days will the work be completed? 

Vikas can do the work in 7 days So, Vikas’ 1 day work = 1/7 Vishal can do the work in 14 days So, Vishal’s 1 day work = 1/14 Together 1 day work: = 1/7 + 1/14 = 2/14 + 1/14 = 3/14 Let total time taken to complete the work = x days Then, For first (x − 4) days, both work together. Work done in (x − 4) days: = (x − 4) × 3/14 For last 4 days, only Vishal works. Work done by Vishal in 4 days: = 4 × 1/14 = 4/14 = 2/7 Total work = 1 So, (x − 4) × 3/14 + 2/7 = 1 Multiply by 14: 3(x − 4) + 4 = 14 3x − 12 + 4 = 14 3x − 8 = 14 3x = 22 x = 22/3 days