Concepts – Probability

Probability is usually expressed as a fraction or decimal. Since the number of ways a certain outcome may occur always smaller or equal to the total number of outcomes, the probability of an event is some number from 0 through 1.

Rules

P (not A) = 1 – P(A)
A probability of 1 means that the event will certainly occur. 
A probability of 0 means that there is no chance the event will occur. 

Example

What is the probability of randomly picking a yellow or pink cube?

Solution

1. Since there is at least one yellow and pink cube in the box, it is possible to pick one of either of those colors. There is at least one other color (green) in the box, so picking one of them isn’t for certain. 

2. As 4 out of the 5 cubes in the box are either pink or yellow, it is likely one of them will be picked.

Answer: Likely

Prerequisite Skills

None