A box contains cards numbered 3, 5, 7, 9, ...., 35, 37. A card is drawn at random from the box. Find the probability that the number on the card is a prime number.
Total numbers of elementary events are: 18
(3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, , 27, 29, 31, 33, 35, 37)
The favourable prime number cards in the box are: 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37
The numbers of favourable outcomes = 11
∴ P (prime number) = P (E) = 11/18