A bag contains 12 bals of different colours: 5 red, 4 blue and 3 yellow. What is the probability of not selecting a red ball

The probability of an event not happening is 1 minus the probability of the event happening. Five of the twelve balls are red so the probability of selecting a red ball is 5/12. The probability of not selecting a red ball is 1 - 5/12. Find a common denominator in order to calculate this subtraction: 1 - 5/12 = 12/12 - 5/12 = 7/12.