Bob can paint a fence in 5 hours and working with jen, the two of them can paint the same fence in 2 hours. how long would it take for jen to paint the fence alone?

Bob ;

5 hours = 1 fence
1 hour = 1/5 fence

Together:
2 hours = 1 fence
1 hour = 1/2 fence

Jen:
1 hour = 1/2 - 1/5= 5/10 - 2/10 = 3/10

Find the amount of time Jen will need:
3/10 fence = 1 hour
1/10 fence = 1/3 hour
10/10 fence = 10/3 hour = 3 1/3 hours 

Answer: Jen will take 3 1/3 hours to paint the fence alone.