A sample of 120 local residents reveals that 8 have a post office box for receiving mail. What is the relative frequency that a local resident does not have a post office box for receiving mail?

In practice, the relative frequency of an event happening is the same as the probability that that event happened. In other words, the terms "relative frequency" and "probability" can be used interchangeably.

Now, the probability P(A) of an event A happening is given by;

P(A) = [tex]\frac{number-of-outcomes-in-the-event-A}{number-of-outcomes-in-the-sample-space}[/tex]

From the question;

The event A is the situation of local residents having a post office box. Therefore the;

number-of-outcomes-in-the-event-A = 8 [since only 8 of the local residents have a post office box]

number-of-outcomes-in-the-sample-space = 120 [since there are altogether 120 local residents]

Therefore,

P(A) = [tex]\frac{8}{120}[/tex]

P(A) = [tex]\frac{1}{15}[/tex]

The relative frequency that a local resident does not have a post office box for receiving a mail is therefore, [tex]\frac{1}{15}[/tex]

PS: Sometimes it is much more convenient to express relative frequencies as percentage. Therefore, the result above expressed in percentage gives:

[tex]\frac{1}{15} * 100%[/tex]% = 6.67%