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Maths FROM 2

Chap12: elementary probability

Definition of probability

Probability is the number of outcomes of an event (possible outcomes) divided by the number of outcomes. The probability of an event (x) occurring is denoted as P(x)

P(x) = number of occurance of an event (x)total of outcomes

 

Ex: a) Given the following numbers 2, 1, 4, 6, 8, 9, 4. Find the probability that a number chosen randomly from the group will be 4.

b) A bag contains 45 balls. Among these 12 are green, 13 are blue and 18 are yellow. Find the probability that a ball chosen at a random will be a blue ball, a yellow ball, a green ball, neither yellow nor green

Solution:

a) Total number of 4s = 2

Total number of elements = 7

P (4) = total number of 4stotal number of elements = 2/7

b)  Total number of balls = 45

Number of blue balls = 15

P(blue balls) = 15/45 = 1/3

Number of yellow balls = 18

P(yellow balls) = 18/45 = 2/5

Number of green balls = 12

P(green balls) = 12/45 = 4/15

Having neither a green ball nor a green ball is another way of saying having a blue ball, since the bag has only 3 colours.

P(neither yellow nor green balls) = P(blue) = 1/3

NB: P(blue) + P(yellow) + P(green) = 1/3 + 2/5 + 4/15 = 1*5+3*2+(1*4)15 = 15/15 = 1

Therefore, the sum of the probability of all events occurring together is 1

par Claude Foumtum


Maths FROM 2












Chap12: elementary probability