Question:
Tickets numbers from 1 to 20 are mixed up and a ticket is drawn at random. What is the probability that the ticket drawn has a number which is a multiple of 3 or 7?
Solution:
GIVEN: Tickets are marked from 1 to 20 are mixed up. One ticket is picked at random.
TO FIND: Probability that the ticket bears a multiple of 3 or 7
Total number of cards is 20
Cards marked multiple of 3 or 7 are 3, 6, 7, 9, 12, 14, 15 and18
Total number of cards marked multiple of 3 or 7 are 8
We know that PROBABILITY = 
Hence probability of getting a, multiple of 3 or 7 is