Question

Bubba can mow a field in 8 hours. If Skeeter helps, they both can do it together in 3 hours. How long would it take Skeeter to mow the field by himself?

Answer 1

When they work together, they do 1/3 of the job in one hour.

(Bubba) + (Skeeter) = 1/3 job/hour

Subtract 'Bubba'
from each side: Skeeter = (1/3 job/hour) - (Bubba)

Bubba, working alone, does 1/8 of the job in one hour.

Skeeter = (1/3 job/hour) - (1/8 job/hour)

Can you subtract 1/8 from 1/3 ?

Before you can subtract, you'll need a common denominator.
I've got a nice one here . . . 24 .

1/3 = 8/24
1/8 = 3/24

Skeeter = (1/3 job/hour) - (1/8 job/hour)

= (8/24 job/hour) - (3/24 job/hour)

= 5/24 job/hour .

Skeeter mows at the rate of 5/24 field/hour.

The other way to look at that is: 24/5 hour/field = 4.8 hours .

Check:

Bubba: 1/8 field per hour = 0.125
Skeeter: 1/4.8 field per hour = 0.208333...

Together: (0.125 + 0.208333)

= 0.333... field per hour

= 3 hours/field . yay!