Thread: Discrete Probability Distribution II

from walpole 5.61

Suppose the probability is 0.8 that any given person wll believe a tale about the transgressions of a famous actress.

a) the sixth person to hear this tale is the forth one to believe it ?
b) what is the probability that the thrd person to hear this tale is the first one to believe it ?

i know p= 0.80 and q = 1- 0.8=0.20

but how should i apply the above to the questions ?
i don't even know how many people are listening to the tale.
pls explain.

Originally Posted by hazel

from walpole 5.61

Suppose the probability is 0.8 that any given person wll believe a tale about the transgressions of a famous actress.

a) the sixth person to hear this tale is the forth one to believe it ?
b) what is the probability that the thrd person to hear this tale is the first one to believe it ?

i know p= 0.80 and q = 1- 0.8=0.20

but how should i apply the above to the questions ?
i don't even know how many people are listening to the tale.
pls explain.

a) is a negative binomial distribution problem.
b) (0.2)(0.2)(0.8) = ....

Hello, Hazel!

Suppose the probability is 0.8 that any given person will believe a rumor of a scandal.

a) What is the probability that the 6th person to hear the rumor is the 4th one to believe it ?

Let = the person believes the rumor.
and = the person does not believe the rumor.


Among the first 5 who heard the rumor, there were 3 B's (and 2 N's).
. . This probability is: .

Then the 6th person is a B: .

Therefore: .

b) What is the probability that the 3rd person to hear this rumor is the first to believe it ?

The first two were N's: .

The third is a B: .

Therefore: .

Originally Posted by Soroban

Hello, Hazel!

Let = the person believes the rumor.
and = the person does not believe the rumor.


Among the first 5 who heard the rumor, there were 3 B's (and 2 N's).
. .

refering to the bold comments above, how do you know 3B and 2 N ?
it can also be other combination ?