What is Probability?
- the likelihood that an event will happen from all the possible outcome.
What is an event?
An “event” can be one or more outcomes.
A dice has 6 faces - 1, 2, 3, 4, 5 and 6.
What a dice is tossed, one of six events can happen:- the number is 1, 2, 3, 4, 5, or 6
Probability
Probability = Positive events / Total number of possible outcomes
Example
When a dice is tossed, what is the probability of having the number 2?
Dice Number 1 2 3 4 5 6
Number(Event) 1 1 1 1 1 1
Probability 1/6 1/6 1/6 1/6 1/6 1/6
=>
Total number of events = 6 [Step1: Total possible outcome]
No. 2 happens = 1 [Step2: Count of positive event ]
Probability of number is 2 = 1/6 [Step3:Compute probability]
Also, probability is
~ expressed as a value between 0 and 1.
~ an event that will not happen at all (0%), probability = 0
~ an event that will definitely happen(100%), probability = 1
~ Sum of Probability of all possible events = 1
Example
There are 2 red balls and 1 blue ball in a basket. What is the probability of picking up a red ball from the basket?
Colour R R B
Event 1 1 1 (total = 3)
Probability 1/3 1/3 1/3
Event of Red = 2, Probability = 1/3+ 1/3 = 2/3 or 2/3
=>
Total events = 3 [Step1: red ball, red ball, blue ball]
Picking a red ball = 2 [Step2: positive event = 2]
Probability = 2/3 [Step3: Compute probability]
Probability with a Frequency Distribution Table
Example
The following is the data of people going to Johore Bahru
Transport Frequency
Walk 40
Train 24
Bus 56
What is the probability of a person walking to Johore Bahru?
Number of people walking = 40 [Step1: positive event]
Total number of people = 40 + 24 + 56 [Step 2: Total]
= 120
Probability = 40/120 = 1/3 [Step 3: Compute]
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