Mr. X can do a job in 8 days and his son can do it in 12 days, How many days will it take them to complete the job if they work together?

For Mr X,

in 8 days, he can do 1 job

in 1 day, he can do 1/8 job

For his son,

in 12 days, he can do 1 job

in 1 day, he can do 1/12 job

If they work together, in 1 day, they can do (1/8 + 1/12) job

                                                                        = (3+2)/24

                                            &nbs