Question

The brand name of Mrs. Fields (cookies) has a 90% recognition rate. If Mrs. fields herself wants to verify that rate by beginning with a small sample of 10 randomly selected consumers, find the probability that exactly 9 of the 10 consumers recognize her brand name. Also, find the probability that the number who recognize her brand name is not nine.

Answer 1

0.3874 = 38.74% probability that exactly 9 of the 10 consumers recognize her brand name.

0.6126 = 61.26% probability that the number who recognize her brand name is not nine.

Explanation:

For each consumer, there are only two possible outcomes. Either they recognize the name, or they do not. The probability of a customer recognizing the name is independent of anu other customer. This means that the binomial probability distribution is used to solve this question.

Binomial probability distribution

The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.

`P(X = x) = C_(n,x).p^(x).(1-p)^(n-x)`

In which
`C_(n,x)` is the number of different combinations of x objects from a set of n elements, given by the following formula.

`C_(n,x) = (n!)/(x!(n-x)!)`

And p is the probability of X happening.

The brand name of Mrs. Fields (cookies) has a 90% recognition rate.

This means that
`p = 0.9`.

Sample of 10

This means that
`n = 10`

Find the probability that exactly 9 of the 10 consumers recognize her brand name.

This is P(X = 9). So

`P(X = x) = C_(n,x).p^(x).(1-p)^(n-x)`

`P(X = 9) = C_(10,9).(0.9)^(9).(0.1)^(1) = 0.3874`

0.3874 = 38.74% probability that exactly 9 of the 10 consumers recognize her brand name.

Also, find the probability that the number who recognize her brand name is not nine.

1(100%) subtracted by those who recognize. So

1 - 0.3874 = 0.6126

0.6126 = 61.26% probability that the number who recognize her brand name is not nine.