Question:
Cards each marked with one of the numbers 4, 5, 6, ..., 20 are placed in a box and mixed thoroughly. One card is drawn at random from the box. What is the probability of getting an even number?
Solution:
GIVEN: Cards are marked with one of the numbers 4, 5, 6…20 are placed in a box and mixed thoroughly. One card is picked at random.
TO FIND: Probability of getting an even number on the picked card.
Total number of cards is 20-3=17
Cards marked even number are 4,6,8,10,12,14,16,18,20
Total number of cards marked even is 9
We know that PROBABILITY = 
Hence probability of getting an even number on the card =