Page 26 - Probability Demystified

CHAPTER 1 Basic Concepts 15

ANSWERS
36 þ 16 þ 3 55 11
1. a. P(40 or older) ¼ ¼ ¼
100 100 20

18 þ 27 45 9
b. P(under 40) ¼ ¼ ¼
100 100 20
27
c. P(between 30 and 39) ¼
100
36 þ 16 52 13
d. P(under 60 but over 39) ¼ ¼ ¼
100 100 25

2. The total number of outcomes in this sample space is 50.

22 11
a. PðAÞ¼ ¼
50 25
7 þ 2 9
b. PðBorABÞ¼ ¼
50 50
19 31
c. P(not O) ¼ 1 ¼
50 50
2 þ 7 9
d. P(neither A nor O) ¼ P(AB or B) ¼ ¼
50 50

89 1
3. P(French fries) ¼ ¼
356 4
8 þ 7 15 21 7
4. P(neither liberal arts nor history) ¼ 1 ¼ 1 ¼ ¼
36 36 36 12

5. P(does not get any news from the Internet) ¼ 1 0.74 ¼ 0.26

Law of Large Numbers

We know from classical probability that if a coin is tossed one time, we
cannot predict the outcome, but the probability of getting a head is 1 2 and
1
the probability of getting a tail is if everything is fair. But what happens if
2
we toss the coin 100 times? Will we get 50 heads? Common sense tells us that