Page 85 - Probability Demystified

74 CHAPTER 4 The Multiplication Rules

13. In a certain group of people, it is known that 40% of the people take
Vitamins C and E on a daily basis. It is known that 75% take Vitamin
C on a daily basis. If a person is selected at random, what is the
probability that the person takes Vitamin E given that the person
takes Vitamin C?

5
a.
13
8
b.
15
3
c.
11
7
d.
12
14. Two dice are tossed; what is the probability that the numbers are the
same on both dice if it is known that the sum of the spots is 6?

2
a.
3
1
b.
6
4
c.
5
1
d.
5

Probability Sidelight

THE LAW OF AVERAGES

Suppose I asked you that if you tossed a coin 9 times and got 9 heads, what
would you bet that you would get on the tenth toss, heads or tails? Most
people would bet on a tail. When asked why they would select a tail, they
would probably respond that a tail was ‘‘due’’ according to the ‘‘law of
averages.’’ In reality, however, the probability of getting a head on the