Ram and Ravi can finish a job in 12 days and 21 days respectively. Ram started the job and after 3 days Ravi joined him. In how many days was the complete job finished.

Explanation:

Ram’s 3 days work = 3×1\12=3\12=1\4

Remaining work = 1−1\4=3\4

Ram and Ravi’s one day work = 1\12+1\21=7+4\84=11\84

11\84 part of work will be done by Ram and Ravi m one day.

3\4 part of work

= 84\11×3\4=63\11=5 8\11 days

Total no. of days = 3+5 8\11=8 8\11 days