Question:
An urn contains 10 red and 8 white balls. One ball is drawn at random. Find the probability that the ball drawn is white.
Solution:
GIVEN: A bag contains10 red, and 8 white balls
TO FIND: Probability that one ball is drawn at random and getting a white ball
Total number of balls 
Total number of white balls is 8
We know that PROBABILITY = 
Hence probability of getting a white ball is 