Question:
There are 30 cards, of same size, in a bag on which numbers 1 to 30 are written. One card is taken out of the bag at random. Find the probability that the number on the selected card is not divisible by 3.
Solution:
GIVEN: Cards are marked with one of the numbers 1 to 30 are placed in a bag and mixed thoroughly. One card is picked at random.
TO FIND: Probability of getting a number not divisible by 3 on the picked card.
Total number of cards is 30
Cards marked number not divisible by 3 is 1,2,4,5,7,8,10,11,13,14,16,17,19,20,22,23,25,26,28,29.
Total number of cards marked numbers not divisible by 3 is 20
We know that PROBABILITY = 
Hence probability of getting a number divisible by 3 on the card = 