There are 11 horses in a race.
in how many ways can the first three positions of the order of the finish occur?
(assume there are no ties.)

11 nCr 3  plugged in a calculator will equal 165 Combinations/Positions 

Anita can paint the shed in 5 hours. If Kris helps her, they can paint the shed in 3 hours. How long would it take Kris to paint the shed alone?

Anita rate = 1/5 job/hr
Together rate = 1/3 job/hr
Kris rate = 1/x job/hr
Equation:
rate + rate = together rate

1/x + 1/5 = 1/3

Multiply thru by 15x to get:
15 + 3x = 5x
2x = 15
x = 7.5 hrs (time for Kris to do the job alone)