Steve takes 6 hours to get the yard work done by himself. If Bill works alone, it takes him 10 hours. How long would it take them working together to do all of the yard work?

How much work is done in an hour by each:

s = 1/6 of the yard in one hourb = 1/10 of the yard in an hour

working together they can do:

1/6 + 1/10 in an hour; or 16/60; we can invert this number to determine how long it takes to finish the yard

60/16 hours

=3 hours and 45 minutes