The 0-to-1 Probability Scale
Understand probability as a measure expressed as a number between 0 (impossible) and 1 (certain); place events on the probability scale; express probabilities as fractions, decimals, and percentages
What a learner can do afterwards
- Place events on a number line from 0 (impossible) to 1 (certain), expressing positions as fractions or decimals
- Explain that a probability of 0.5 means 'even chance' and connect this to the informal word 'likely'
- Convert between informal language ('very unlikely') and a numerical position on the 0-to-1 scale
The lesson
Probability is a number that tells you how likely something is to happen. It always sits somewhere between 0 and 1. An event that can never happen has a probability of 0. An event that will always happen has a probability of 1.
A weather app shows a 5 in 10 chance of rain today. That's the same as 0.5. Because 0.5 sits right in the middle of the scale, rain and no rain are equally likely - an even chance.
You can write the same probability three ways: as a fraction like 1/2, as a decimal like 0.5, or as a percent like 50%. Numbers close to 0 mean 'very unlikely.' Numbers close to 1 mean 'very likely.'
Every probability lands somewhere between 0 (impossible) and 1 (certain), and that same spot can be written as a fraction, a decimal, or a percent.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.