Basic Probability
Probability measures how likely an event is on a scale from 0 to 1.
About this topic
Probability measures how likely an event is, from 0 (impossible) to 1 (certain). For equally likely outcomes, P(event) = favourable outcomes / total outcomes. The probabilities of all outcomes in the sample space add to 1, and P(not A) = 1 − P(A).
Experimental probability comes from repeated trials, while theoretical probability comes from reasoning about the outcomes. The law of large numbers says experimental results approach theoretical ones as the number of trials grows. For events that cannot happen together, called mutually exclusive, P(A or B) = P(A) + P(B); otherwise subtract the overlap, P(A or B) = P(A) + P(B) − P(A and B).
Example: rolling a fair die, P(even) = 3/6 = 1/2, and P(not a six) = 5/6. Rolling two dice gives 36 equally likely outcomes, and a total of 7 appears in 6 of them, so P(7) = 1/6, the most likely sum.
Probability underlies weather forecasts, insurance, medical testing and games. A common misconception is the gambler's fallacy: after five heads in a row, the next flip is still 50% heads, because coins have no memory.
Key ideas
- P = favorable ÷ total outcomes
- 0 is impossible, 1 is certain
- P(not A) = 1 − P(A)
Quick check
Use cases: where Basic Probability helps
- Homework: review the key idea behind Basic Probability before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Basic Probability without notes.
- Visual learning: play with the interactive lab to see how Basic Probability changes when you adjust its inputs.
- Teaching a friend: explain Basic Probability in your own words, then compare your version with the key ideas.
Number and algebra skills are used in science, engineering, budgeting and computing.
Frequently asked questions
What is Basic Probability?
Probability measures how likely an event is on a scale from 0 to 1.
What will I learn in Basic Probability?
P = favorable ÷ total outcomes. 0 is impossible, 1 is certain. P(not A) = 1 − P(A).
Is Basic Probability part of Mathematics?
Yes. It is one of 200 Mathematics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Basic Probability lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Basic Probability?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.