Probability

Question 1

How do you calculate the probability of an event?

Answer 1

Number of ways the event can happen/total number of events that can happen

Question 2

What does mutually exclusive mean?

Answer 2

If two events cannot happen at the same time they are mutually exclusive

Question 3

Give an example of a mutually exclusive event

Answer 3

Flipping a coin and getting heads and tails, rolling a dice and it lands on 1 and 3, etc

Question 4

How do you calculate the probability an event doesn’t happen?

Answer 4

1 - The probability it does happen

Question 5

What is theoretical probabilty?

Answer 5

The probability to be expected with infinite trials

Question 6

Give an example of theoretical probability

Answer 6

Flipping a coin and getting heads=1/2, or 0.5

Question 7

What is experimental probability?

Answer 7

The probability based on the data from an experiment.

Question 8

What is another name for experimental probability?

Answer 8

Relative frequency?

Question 9

Example 1 -

Joe’s Christmas present list from his family for the past 15 years

Gift Frequency

Money                         6
Electronics/games     7
Lynx Africa                  4
Clothes                       8
Toys                            3
Others                        5

a. What is the probability Joe gets Lynx Africa?
b. Calculate the relative frequency of Joe receiving money for Christmas

Answer 9

a. 4/33

b. 6/33

Question 10

Example 2 -

The probability that a biased dice will land on a 6 is 0.3
The dice is going to be rolled 200 times
Work out an estimate for the number of times the dice will land on 6

Answer 10

0.3=30%
30% of 200=60 times
Note: do not write 60/200. This is not a probability but a ‘number of times’ an event will happen

Question 11

Example 3 -

A biased spinner can land on red, blue, yellow and green
The table shows the probabilities that the spinner will land on red, blue and yellow.

Color Red Blue Yellow Green
Probability 0.3 0.25 0.15

a. Complete the table

Kelly is going to spin the spinner 60 times
b. Work out an estimate for the number of times the spinner will land on red.

Answer 11

a. 0.3+0.25+0.15=0.7
1-0.7=0.3
Green=0.3
b. 30% of 60=18 times

Question 12

Example 4 -

In a bag there are only red counters, blue counters and white counters
A counter is taken at random from the bag
The table shows the probability of getting a red counter

Colour Red Blue White
Probability 0.2

The probability of getting a blue counter is the same probability as getting a white counter
a. Complete the table

There are 18 red counters in the bag
b. Work out the total number of counters in the bag

Answer 12

a. 1-0.2=0.8
0.8/2=0.4
Blue=0.4
White=0.4
b. 20% of counters are red
18 red counters are in the bag
1–%=18x5=900
900 counters in total are in the bag