A jar contains 6 chocolate chip cookies and 9 peanut butter cookies. Richard grabs 3 cookies at random to pack in his lunch. What is the probability that he drew 2 chocolate chip cookies and 1 peanut butter cookie?

Verified Answer :

The answer is 0.096.


To calculate this, a multiplication rule is used. The multiplication rule calculates the probability that both of two events will occur.


There are in total 15 cookies in the jar:
6 chocolate chip cookies + 9 peanut butter cookies = 15 cookies


The probability to drew 1 chocolate chip cookie is: \(P_1= \frac{6}{15} = \frac{2}{5}\)
The probability to drew 1 peanut butter cookie is: \(P_2= \frac{9}{15} = \frac{3}{5}\)


In this example, we have three events occurring together:
1. The probability that he drew 1 chocolate chip cookie: \(P_1= \frac{2}{5}\)
2.The probability that he drew 1 chocolate chip cookie: \(P_1= \frac{2}{5}\)
3. The probability that he drew 1 peanut butter cookie: \(P_2= \frac{3}{5}\)


By using the multiplication rule, the probability that he drew 2 chocolate chip cookies and 1 peanut butter cookie is 0.096:
\(P=P_1*P_1*P_3= \frac{2}{5} * \frac{2}{5} * \frac{3}{5} = \frac{2*2*3}{5*5*5} = \frac{12}{125} = 0.096\)