A box contains 19 balls bearing numbers 1, 2, 3 ..., 19 respectively. A ball is drawn at random from the box. Find the probability that the number on the ball is (i) a prime number (ii) an even number (iii) a number divisible by 3.
(i) Total number of ball bearings = 19
Chances of drawing a prime numbered ball = 9 (They are 2,3,5,7,11,13,17,19)
Probability P() = 
Probability of drawing a prime numbered ball bearing P(prime ball)
= 
= 
(ii) Total number of ball bearings = 19
Chances of drawing an even numbered ball = 9 (They are 2,4,6,8,10,12,14,16,18)
Probability P() = 
Probability of drawing an even numbered ball bearing P(even ball)
= 
= 
(iii) Total number of ball bearings = 19
Chances of drawing a numbered ball which is divisible by 3 =6 (They are 3,6,9,12,15,18)
Probability P() = 
Probability of drawing a numbered ball bearing which is divisible by 3 P(ball divisible by 3)
= 
= 