Trey buys a bag of cookies that contains 4 chocolate chip cookies, 6 peanut butter cookies, 7 sugar cookies and 7 oatmeal cookies.What is the probability that Trey reaches in the bag and randomly selects a sugar cookie from the bag, eats it, then reaches back in the bag and randomly selects an oatmeal cookie? Give your answer as a fraction, or accurate to at least 4 decimal places.

Respuesta :

Solution

The total number nof cookies in the bag is:

[tex]4+6+7+7=24\text{ cookies}[/tex]

- Thus, we can write the probabilities of choosing any of the cookies are given as:

[tex]\begin{gathered} P(\text{chocolate chip)}=\frac{4}{24} \\ \\ P(\text{Peanut Butter)}=\frac{6}{24} \\ \\ P(\text{Sugar Cookies)}=\frac{7}{24} \\ \\ P(\text{Oatmeal)}=\frac{7}{24} \end{gathered}[/tex]

- Now, let us analyze Trey's random choices

Choice 1:

He chose a sugar cookie at first.

- Thus, the probability of this choice is

[tex]P(\text{Sugar Cookies})=\frac{7}{24}[/tex]

Choice 2:

- He chose an oatmeal cookie in the second choice.

- But he already had one cookie before this choice, thus, the total number of cookies is one less. That is, 23 not 24.

- Thus, the probability of choosing the oatmeal cookie is given as:

[tex]P(\text{Oatmeal)}=\frac{7}{23}[/tex]

- Because these choices do not interfere with one another (i.e. they are mutually exclusive), we can apply the AND probability formula to calculate the probability that Treys chose a Sugar Cookie first, and then an Oatmeal cookie next.

- The AND probability is given as

[tex]P(A\text{ AND }B)=P(A)\times P(B)[/tex]

- Thus, we can find the probability that Trey chooses Sugar Cookies first and Oatmeal Cookie next as follows:

[tex]\begin{gathered} P(\text{Sugar Cookies AND Oatmeal)}=\frac{7}{24}\times\frac{7}{23} \\ \\ P(\text{Sugar Cookies AND Oatmeal)}==\frac{49}{552} \end{gathered}[/tex]

Final Answer

The answer is

[tex]P(\text{Sugar Cookies AND Oatmeal)}==\frac{49}{552}[/tex]