A box has 5 red balls and 10 blue balls numbered with “1”, 10 red balls and 15 blue numbered with 2. What is the probability that one will be chosen will be a red ball or numbered “1”?

Answer 1

P(red or "1") = P(red) + P("1") - P(red and "1") = 15/40 + 15/40 - 5/40 = 25/40 = 0.625

Answer 2

P(red) + P(1) - P(red and 1)