Example 3
In a certain population of caribou, the probability of a caribou being sickly is 0.4. If a caribou is sickly, the
probability wolves eat it is 0.3. If a caribou is not sickly, the probability wolves eat it is 0.2. If a caribou is
chosen at random from the herd, answer the following questions.
a. Create a tree diagram before answering the questions below.
Note & sum of each group of branches must equal 1
* Second colum of branches are conditional probability
* Multiply across to get the "AND's"
Sick
0.4 eat/sick 0.3 = 0.12
Not eat/sick 0.7 = 0.28
well
0.6 eat/well 0.2 = 0.12
Not eat/well 0.8 = 0.48
b. What is the probability of the caribou being sickly and not being eaten by wolves?
0.28
c. What is the probability of the caribou not being eaten by wolves?
d. If a caribou is sickly, what is the probability that it will be eaten by wolves?
0.3
e. If wolves ate a caribou, what is the probability that it was sickly?