A bag contains 3 red balls and 5 black balls. A ball is drawn at random from the bag. What is the probability that the ball drawn is not red?

The correct answer is $\frac{5}{8}$

As the ball is drawn at random, all the balls have equal chance of getting drawn.
∴ Number of possible outcomes = 3 + 5 = 8
Let E denote the outcome where the ball is red.
∴ Number of outcomes favourable to event E = 3
∴ Probability of event E = $\frac{3}{8}$
∴ Probability of event not being E = 1 - $\frac{3}{8}$ = $\frac{5}{8}$