Question

quiz 6.4.1 - adding probabilities
this quiz will test your knowledge on when and how to add probabilities together.
value: 3
a magazine contains twelve pages. you open to a random page. what is the probability that the page number is nine or eleven?
a. 1/144
b. 1/6
c. 1/12
d. 9/11

Explanation:

Step1: Find probability of page 9

The probability of opening to page 9 is $\frac{1}{12}$ since there is 1 page numbered 9 out of 12 total pages.

Step2: Find probability of page 11

The probability of opening to page 11 is $\frac{1}{12}$ since there is 1 page numbered 11 out of 12 total pages.

Step3: Use addition rule for mutually - exclusive events

Since getting page 9 and getting page 11 are mutually - exclusive events, the probability of getting page 9 or 11 is $P(9\ or\ 11)=P(9)+P(11)$. So $P(9\ or\ 11)=\frac{1}{12}+\frac{1}{12}=\frac{2}{12}=\frac{1}{6}$.

Answer:

B. 1/6