Question: Please show me the solution for: 20% of 50 people think horse #2 will win the big race.  60% of the remaining people think horse #7 will win.  The rest of the people think horse #12 will win the big race.  How many people think that horse #12 will win?
Answer: 
20% of 50 people are pulling for horse #2 so that's .20*50 = 10 people
10 out of 50 people think horse #2 will win which leaves 50-10 = 40 people
60% of 40 people think horse #7 will win so that's .60*40 = 24 people
That leaves 40-24 = 16 people that think horse #12 will win