If you complete a job in 20 minutes, the same job your brother completes in 30 minutes. Then you both complete the same job together?

If you complete a job in 20 minutes, the same job your brother completes in 30 minutes. Then you both complete the same job together?

Solution:

You complete a job: 20 minutes 

your completes the same job: 30 minutes

You both complete the same job: ???

∴ 1/20+ 1/30

Take L.C.M of 20 and 30 will be 60

3/60+2/60

∴ 3+2=5

5/60

1/12

you and your brother will complete the job in 12 minutes