Question

Inside the box of every cereal box contains a surprise gift. The store manager assures employees that 22 of the 45 boxes on the shelf have a secret decoder ring and inside the other 23 boxes on the shelf contain a different gift. If two cereal boxes are randomly selected from the shelf to purchase, what is the probability that both of them have the secret decoder ring

Answer 1

Answer:

0.2333 = 23.33% probability that both of them have the secret decoder ring

Step-by-step explanation:

The cereals are chosen without replacement, which means that the hypergeometric distribution is used to solve this question.

Hypergeometric distribution:

The probability of x successes is given by the following formula:

$P(X = x) = h(x,N,n,k) = \frac{C_{k,x}*C_{N-k,n-x}}{C_{N,n}}$

In which:

x is the number of successes.

N is the size of the population.

n is the size of the sample.

k is the total number of desired outcomes.

Combinations formula:

$C_{n,x}$ is the number of different combinations of x objects from a set of n elements, given by the following formula.

$C_{n,x} = \frac{n!}{x!(n-x)!}$

In this question:

45 boxes, which means that $N = 45$

22 have the secret decoder ring, which means that $k = 22$

Two boxes, which means that $n = 2$

What is the probability that both of them have the secret decoder ring?

This is P(X = 2). So

$P(X = x) = h(x,N,n,k) = \frac{C_{k,x}*C_{N-k,n-x}}{C_{N,n}}$

$P(X = 2) = h(2,45,2,22) = \frac{C_{22,2}*C_{23,0}}{C_{45,2}} = 0.2333$

0.2333 = 23.33% probability that both of them have the secret decoder ring