I believe the probability of either event A or B occurring is
which in this case is
A poll found that the probability that a student chosen at random had visited the arcade within the past week was 0.3. The probability that a student chosen at random played games on a home-based game machine was 0.5. The probability that a student did both was 0.2. What was the probability that a student played on an arcade machine or on a home-based machine?
Thanks in advance!
0.3=P(plays on arcade machine)=P(plays only on arcade machine)+P(plays on arcade and home machine)
0.5=P(plays on home machine)=P(plays at home only)+P(plays at home and at arcade)
0.3+0.5=P(arcade only)+P(home only)+2P(both)
0.8=P(plays either one)+P(both)
P(plays either one)=0.8-0.2