Page 24 - Probability Demystified

CHAPTER 1 Basic Concepts 13

SOLUTION:

The probability is 7%.

EXAMPLE: In a sample of 642 people over 25 years of age, 160 had a
bachelor’s degree. If a person over 25 years of age is selected, find the
probability that the person has a bachelor’s degree.

SOLUTION:

In this case,
160
Pðbachelor’s degreeÞ¼ ¼ 0:249 or about 25%:
642

EXAMPLE: In the sample study of 642 people, it was found that 514 people
have a high school diploma. If a person is selected at random, find the
probability that the person does not have a high school diploma.

SOLUTION:
The probability that a person has a high school diploma is

514
P(high school diploma) ¼ ¼ 0:80 or 80%:
642
Hence, the probability that a person does not have a high school diploma is

P ðno high school diplomaÞ¼ 1 Pðhigh school diplomaÞ
¼ 1 0:80 ¼ 0:20 or 20%:

Alternate Solution:
If 514 people have a high school diploma, then 642 514 ¼ 128 do not have a
high school diploma. Hence
128
Pðno high school diplomaÞ¼ ¼ 0:199 or 20% rounded:
642
Consider another aspect of probability. Suppose a baseball player has a
batting average of 0.250. What is the probability that he will get a hit the next
time he gets to bat? Although we cannot be sure of the exact probability, we
1
can use 0.250 as an estimate. Since 0:250 ¼ , we can say that there is a one
4
in four chance that he will get a hit the next time he bats.