A roulette wheel consists of 38 slots. 36 of these are
numbered 1 through 36 and colored red or black so
that there are nine red even-numbered slots, nine black
odd-numbered slots, etc. These slots occur with equal
probability. The two slots marked 0 or 00 are each
three times as likely to occur as any one of the other
36. What is the probability that a red even number, a
red 23, or a 00 will occur on one roll of the wheel?


The answer is 13/42.

Someone please explain this to me, thanks.