Step 6 Objective

Know that if the probability of an event occurring is p, then the probability of it not occurring is 1 – p.

Examples of what pupils should know and be able to do

Pupils should be able to answer questions such as:

Given a set of snooker balls (15R, Y, G, Br, Bl, P, BK), if one ball is chosen at random what is the chance that it is:

  1. red?
  2. not red?
  3. black?
  4. not black?

Probing questions

If the probability of scoring less than 3 on an ordinary six-sided fair dice is 2/6 how would we describe the event which has the probability 4/6?

What if pupils find this a barrier?

Use events where it is possible to show all outcomes, e.g. dice or digit cards.

Using the digit cards numbered 0–9 lay them out so that the numbers can be seen. Ask pupils how many cards show numbers worth less than 3. How many show numbers worth 3 or more? Convert these numbers into probabilities, e.g. What is the probability of showing a number with value less than 3? What is the probability of choosing a card that shows a number with value 3 or more?