Monitor three consecutive phone calls going through a telephone switching office. Classify each one as a voice call (v) if someone is speaking or a data call (d) if the call is carrying a modem or fax signal. Your observation is a sequence of three letters (each letter is either v or d). For example, two voice calls followed by one data call corresponds co vvd.

a) Write the elements of the following sets: A1= {first call is a voice call} B1= {first call is a data call} A2= {second call is a voice call} B2= {voice and data alternate}

b) For the first pair of events A1 and B above, identify whether the pair of events is either mutually exclusive or collectively exhaustive.