Question
An urn contains 25 balls numbered 1 to 25. Two balls are drawn from the urn with replacement. Find the probability of getting no odd number.
Solution
Total number of balls = 25
∴ Total number of cases = 25
Let E denote the event of drawing even numbered ball and O denote the event of drawing odd numbered ball.
Number of balls numbered odd = 13
Number of balls numbered even = 12
Probaility of getting both the balls even numbered
= P(EE) = P(E) P(E) = 
P(at least one odd) = 1 - P(EE) = 1 - 
P(no. odd number) = 1 - P(at least one odd) = 
