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Example 1
• In a group of 8 pupils, there was a chance for one of them
to be chosen a group leader. Give that chance in numerical figure. Example 2 of 15 men, 7 were to be given presents. • From a group What was the probability that any of them would get a present? Example 3 were pieces of chalk, 6 red, 5 blue • In a box, there and 7 green. If a piece of chalk was to be picked without looking into the box, what would be the probability that the piece is (a) red (b) green Exercise 1. In a box, there are some pencils of different colours; 8 black, 4 red and 6 brown ones. What would be the probability of choosing a (i) brown pencil (ii) black pencil 2. From the numbers, 7, 3, 4, 5, 1, what would be the probability of choosing (i) a 6 (ii) a 7 (iii) two numbers whose total is 8? 3. There are some cars of different colours, ( 7 maroon, 8 black and 5 green. What is the probability of picking a car of black colour at random? THURSDAY 18TH NOVEMBER 2021
PRIMARY SIX MATHEMATICS
CALCULATING PROBABILITY FROM VENN DIAGRAMS
NOTES: Probability is a fraction whose numerator is the number of expected chances and the denominator is the total number of all chances. The number of members in given sets forms the total number of chances in a Venn diagram. Example 1 The Venn diagram represents the number of members in sets A and B. Calculate the probability of choosing a number in A n B. Example 2 Calculate the probability of choosing a member in P’. EXERCISE Calculate the probability of choosing a member from the named set. CALCULATING PROBABILITY USING A VENN DIAGRAM • SOLVING PROBABILITY PROBLEMS IN A SET NEEDS WRITING THE EXPECTED SET AS A FRACTION OF THE UNIVERSAL SET. EXAMPLE 1 • In a dozen of members, 7 can sing (s), 8 can dance (d), and 3 can both sing and dance. What is the probability of choosing a member that can only dance? EXAMPLE 2 • In a class of 20 pupils, 15 eat meat (M), 10 eat fish (F), 2 do not eat any of the two, but x eat both. What is the probability of choosing at random a pupil who eats both meat and fish?