A building may fail by excessive settlement of the foundation or by collapse of the superstructure. Over the life of the building, the probability of excessive settlement of the foundation is estimated to be 0.10, whereas the probability of collapse of the superstructure is 0.05. Also, if there is excessive settlement of the foundation, the probability of superstructure collapse will be increase to 0.20.

A) What is the probability that building failure will occur over its life?
B) If building failure should occur during its life, what is the probability that both failure modes will occur?
C) What is the probability that only one of the two failure modes will occur over the life of the building?