algebra
posted by jj .
Bob mosw his lawn in 3 hours, Jane can mow the same lawn in 5 hours. How much time would it take for them to mow the lawn together?

This is a problem in which you need to convert the work rate into something addable.
If Bob does his lawn in 3 hours, he does 1/3 in one hour. Similarly Jane can mow 1/5 of the lawn in one hour.
So in one hour, both working together will mow (1/3)+(1/5)=8/15 of the lawn.
The time it takes to mow the complete lawn is therefore 1/(8/15)=15/8=1 7/8 hours. 
Thank you so much!

You're welcome!