A box contains 4 red, 5 green and 6 black balls. A ball is drawn at random from the box. What is the probability that the ball drawn is either red or black?

Question: A box contains 4 red, 5 green and 6 black balls. A ball is drawn at random from the box. What is the probability that the ball drawn is either red or black?

Solution:
Total number of balls = (4 + 5 + 6) = 15
P(drawing a red ball or a black ball) = P(red) + P(black)
= (4/15) + (6/15)
= (4 + 6)/15
= 10/15
= 2/3
∴ The probability is 2/3.