Subject: mathqa
Question: the probability that event b occurs is 0.6 , and the probability that events a and b both occur is 0.25 . if the probability that either event a or event b occurs is 0.4 , what is the probability that event a will occur ?
Option: 
A: 0.55
B: 0.45
C: 0.15
D: 0.05
Answer: D