Stickels Puzzle #47

I can mow my lawn in 2 hours. My son can mow the same lawn in 2.5 hours. If we both work together, how long will it take us to mow the lawn? 1/3 hour 4/9 hour 5/9 hour 2/3 hour 7/9 hour 8/9 hour 1 hour 10/9 hours 11/9 hours None of the above are correct view results