Answer:
(a) The probability that a randomly selected parcel arrived late is 0.026.
(b) The probability that a parcel was late was being shipped through the overnight mail service A₁ is 0.615.
(c) The probability that a parcel was late was being shipped through the overnight mail service A₂ is 0.192.
(d) The probability that a parcel was late was being shipped through the overnight mail service A₃ is 0.192.
Step-by-step explanation:
Consider the tree diagram below.
(a)
The law of total probability sates that: ![P(A)=P(A|B)P(B)+P(A|B')P(B')](https://tex.z-dn.net/?f=P%28A%29%3DP%28A%7CB%29P%28B%29%2BP%28A%7CB%27%29P%28B%27%29)
Use the law of total probability to determine the probability of a parcel being late.
![P(L)=P(L|A_{1})P(A_{1})+P(L|A_{2})P(A_{2})+P(L|A_{3})P(A_{3})\\=(0.04\times0.40)+(0.01\times0.50)+(0.05\times0.10)\\=0.026](https://tex.z-dn.net/?f=P%28L%29%3DP%28L%7CA_%7B1%7D%29P%28A_%7B1%7D%29%2BP%28L%7CA_%7B2%7D%29P%28A_%7B2%7D%29%2BP%28L%7CA_%7B3%7D%29P%28A_%7B3%7D%29%5C%5C%3D%280.04%5Ctimes0.40%29%2B%280.01%5Ctimes0.50%29%2B%280.05%5Ctimes0.10%29%5C%5C%3D0.026)
Thus, the probability that a randomly selected parcel arrived late is 0.026.
(b)
The conditional probability of an event A provided that another event B has already occurred is:
![P(A|B)=\frac{P(B|A)P(A)}{P(B)}](https://tex.z-dn.net/?f=P%28A%7CB%29%3D%5Cfrac%7BP%28B%7CA%29P%28A%29%7D%7BP%28B%29%7D)
Compute the probability that a parcel was late was being shipped through the overnight mail service A₁ as follows:
![P(A_{1}|L)=\frac{P(L|A_{1})P(A_{1})}{P(L)} \\=\frac{0.04\times 0.40}{0.026} \\=0.615](https://tex.z-dn.net/?f=P%28A_%7B1%7D%7CL%29%3D%5Cfrac%7BP%28L%7CA_%7B1%7D%29P%28A_%7B1%7D%29%7D%7BP%28L%29%7D%20%5C%5C%3D%5Cfrac%7B0.04%5Ctimes%200.40%7D%7B0.026%7D%20%5C%5C%3D0.615)
Thus, the probability that a parcel was late was being shipped through the overnight mail service A₁ is 0.615.
(c)
Compute the probability that a parcel was late was being shipped through the overnight mail service A₂ as follows:
![P(A_{2}|L)=\frac{P(L|A_{2})P(A_{2})}{P(L)} \\=\frac{0.01\times 0.50}{0.026} \\=0.192](https://tex.z-dn.net/?f=P%28A_%7B2%7D%7CL%29%3D%5Cfrac%7BP%28L%7CA_%7B2%7D%29P%28A_%7B2%7D%29%7D%7BP%28L%29%7D%20%5C%5C%3D%5Cfrac%7B0.01%5Ctimes%200.50%7D%7B0.026%7D%20%5C%5C%3D0.192)
Thus, the probability that a parcel was late was being shipped through the overnight mail service A₂ is 0.192.
(d)
Compute the probability that a parcel was late was being shipped through the overnight mail service A₂ as follows:
![P(A_{3}|L)=\frac{P(L|A_{3})P(A_{3})}{P(L)} \\=\frac{0.05\times 0.10}{0.026} \\=0.192](https://tex.z-dn.net/?f=P%28A_%7B3%7D%7CL%29%3D%5Cfrac%7BP%28L%7CA_%7B3%7D%29P%28A_%7B3%7D%29%7D%7BP%28L%29%7D%20%5C%5C%3D%5Cfrac%7B0.05%5Ctimes%200.10%7D%7B0.026%7D%20%5C%5C%3D0.192)
Thus, the probability that a parcel was late was being shipped through the overnight mail service A₃ is 0.192.