Cross County Bicycles makes two mountain bike models, the XB-50 and the YZ-99, in three distinct colors. The following table shows the production volumes for last week:

a. Based on the relative frequency assessment method, what is the probability that a mountain bike is brown?
b. What is the probability that the mountain bike is a YZ-99?
c. What is the joint probability that a randomly selected mountain bike is a YZ-99 and brown?
d. Suppose a mountain bike is chosen at random. Consider the following two events: the event that model YZ-99 is chosen and the event that a white product is chosen. Are these two events mutually exclusive? Explain.