You are going to draw a random marble from a bag containing 5 red marbles, 8
green marbles and two blue marbles. 
Question: What is the probability that you draw a red marble?

There are 5 ways you could succeed (by drawing one the 5 red marbles)

There are 10 ways you could fail (by drawing one of the 8 green marbles or
either one of the 2 blue marble).

                         Number of ways to succeed
Probability = ---------------------------------------------------- 
               Number of ways to succeed + number of ways to fail

         5        5     1
   = -------- = ---- = ---
      5 + 10     15     3

What are the odds that you draw a blue marble?

There are 2 ways you could succeed (by drawing either one the 2 blue marbles)

There are 13 ways you could fail (by drawing one of the 5 red marbles or one
of the 8 green marble).

Odds in Favor = (Number of ways to succeed) TO (Number of ways to fail

              = 2 TO 13

(If you had been asked for the odds against, the answer would have been
13 to 2)

Edwin