Suppose you tell a story to two of your friends. Some people repeat the story to two others, and in turn some of these pass the story on. Each time the story is told, it is told to two new people and no one hears the story twice. Sometime later, it turns out that 384 people have heard the story, but not related it to others. How many people have heard the story from others?
A)766
B)767
C)768
D)769

Question

Quizplus · Accepted Answer

The number of people who have heard the story from others is 2^n - n - 1, where n is the number of times the story has been told. In this case, n = 9, so the number of people who have heard the story from others is 2^9 - 9 - 1 = 512 - 9 - 1 = 502. Adding this to the number of people who have heard the story but not related it to others (384), we get a total of 502 + 384 = 886 people who have heard the story.

Suppose You Tell a Story to Two of Your Friends