EXAMPLE 3.3.2

Referring to the earlier example (from Unit 3 Module 3) concerning the National Requirer:

What is the probability that a randomly selected story will be about Elvis?

The editorial board of the National Requirer has decided to launch two new series of

investigative reports. One series will involve the theme

"Elvis ____ my ____!"

For this series, the writers will generate a story line by filling in the first blank with an item from

this list:

"loved"; "sang to"; "got sick on"; "smoked" and filling in the second blank with an item from

this list:

"fig tree"; "living room carpet"; "cat".

The other series will involve the theme "Aliens ____ my ____!"

The writers will generate a story line by filling in the first blank with an item from this list:

"attacked"; "rescued"; "probed";

and filling in the second blank with an item from this list:

"home town"; "trailer park"; "granny's arrest record"

SOLUTION

First we determine the number of possible story lines.

A story line is either an Elvis story line or an alien story line.

The number of Elvis story lines is (4)(3) = 12

The number of alien story lines is (3)(3) = 9

The total number of story lines is 12 + 9.

Of these, 12 are about Elvis, so

P(story is about Elvis) = 12/21 or approximately .57.