If two events are collectively exhaustive, what is the probability that one or the other occurs?

If two events are collectively exhaustive, what is the probability that one or the other occurs?
 a. 0.00
  b. 0.50
  c. 1.00
  d. Cannot be determined from the information given.

Q. 2

If an experiment consists of five outcomes with P(O1) = 0.10, P(O2) = 0.20, P(O3) = 0.30, P(O4) = 0.25, then P(O5) is
 a. 0.75
  b. 0.15
  c. 0.50
  d. Cannot be determined from the information given.

Q. 3

Which of the following is a requirement of the probabilities assigned to outcome Oi?
 a. P(Oi)  0 for each i c. 0  P(Oi)  1 for each i
  b. P(Oi)  1 for each i d. P(Oi) = 1 for each i

Q. 4

A sample space of an experiment consists of the following outcomes: 1, 2, 3, 4, and 5 . Which of the following is a simple event?
 a. At least 3 c. 3
  b. At most 2 d. 15