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Probability

Probability is about uncertainty and how to assign numbers to uncertainty given some information about the particular situation. It may be necessary to find the sample space for two independent events (see question below) and use this sample space to calculate the probability of a particular outcome by taking the number of successful outcomes and dividing by the total number of outcomes.

Sample question 1

Jack rolls a fair die and spins a fair spinner as shown.

(a) Complete the table below showing all possible outcomes.

(b)How many possible outcomes are there?

24

(c)How many outcomes consist of an odd number and B?

3

(d)What is the probability that an outcome will contain an even number?

1

2

Sample Question 2

Mary has a bag of marbles. The number of marbles of each colour is: 7 yellow, 3 green, 4 red and 2 black.

(a) How many marbles are in the bag?

7 + 3 + 4 + 2 = 16

Mary takes a marble from the bag at random

(b)Complete the sentence below:

The probability that Mary will take a red marble is ª.

(c)"The probability of taking a red marble is greater than the probability of taking a yellow marble." Is this statement correct? Give a reason for your answer.

Reason: There are more yellow marbles than red ones.

Mary found five more black marbles and added them to the bag.

(d)Fill in the number of marbles of each colour in the bag after she has done this.

Contents:

7 yellow marbles

3 green marbles

4 red marbles

7 black marbles

(e)Mary takes a marble from the bag at random. What is the probability that she will take a black marble from the bag?

7

21