Ben takes 6hrs to get a job done & Ted takes 11hrs to get the same job done. If they work together how long will it take them?

Answer 1

What can be added is the rate of work.
This is how much work each finishes in an hour.

Ben's rate + Ted's rate
= 1/6+1/11
= 17/66
Together they do 17/66 of the work in an hour.

So time it takes to get the work done
= 1/(17/66)
= 66/17
= 3 15/17 hours