Chance and probability S1.3 Core Plenary Do you agree with these statements? If not, explain why. The weather can be ‘rainy’ or ‘not rainy’ – there are just two outcomes. So the probability that it will rain tomorrow is 50%. Your school team can either win, lose or draw its next match. So their probability of beating Real Madrid is . Preamble This activity illustrates that the deceptively simple probability formula is valid only for equally likely outcomes. Pupils tend to forget this caveat. Possible content Fuller understanding of the standard probability formula. Resources None. Solutions/Notes Depending on the group, it could be appropriate to consider probabilistic weather forecasts (at the time of writing these are being piloted by the BBC, but are common in the US). As an alternative, the class or small groups could play the game Higher or Lower. This game uses a set of ten cards showing the digits 0 to 9. These are shuffled and arranged face-down in a line. The first card is then turned face-up and pupils guess whether the digit on the next card will be higher or lower than this card. The next card is then turned over and pupils gain a point if their ‘guess’ was correct. This is repeated until all cards are face-up. (The game can easily be adapted for use with a PC projector or OHP to involve the whole class.) Discussion about strategy is essential here.