---
title: "The 0-to-1 Probability Scale"
description: "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"
canonical: https://lightmysky.com/learn/mathematics/the-0-to-1-probability-scale-mt_t0g2SlP404
source: https://lightmysky.com/learn/mathematics/the-0-to-1-probability-scale-mt_t0g2SlP404.md
retrieved: 2026-10-19
---

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# 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

Subject: Mathematics · Area: Probability · Ages 10 to 11
Page: https://lightmysky.com/learn/mathematics/the-0-to-1-probability-scale-mt_t0g2SlP404

## Ready when they can

- 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 that values above 0.5 match the informal word 'likely'
- Convert between informal language ('very unlikely') and a numerical position on the 0-to-1 scale

## Lesson: The 0-to-1 probability scale

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.

*(drawing: 0 tenths is 0: impossible. 5 tenths is 0.5: an even chance. 10 tenths is 1: certain.)*

**Example.** A weather app shows a 5 in 10 chance of rain today. That's the same as 1/2, 0.5, or 50%. Because 0.5 sits right in the middle of the scale, rain and no rain are equally likely, which is an even chance.

*(drawing: Half shaded is 1 out of 2, which is 0.5, or 50%. That's an even chance.)*

The same chance can be written three ways: a fraction such as 6/10, a decimal such as 0.6, or a percent such as 60%. Percent means out of 100, so 40% is 40/100, which is 0.4, and 35% is 35/100, which is 35 hundredths, written 0.35. Words match places on the scale. Close to 0 is very unlikely. Below 0.5 is unlikely. Exactly 0.5, which is 1/2 or 50%, is an even chance. Above 0.5 is likely. Close to 1 is very likely.

**Recap.** 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.

## Practice

16 questions on this page, each with its working shown.

## Needs first

- [Probability as a Fraction](https://lightmysky.com/learn/mathematics/probability-as-a-fraction-mt_-c4Ca_nBzX)
- [Comparing fractions](https://lightmysky.com/learn/mathematics/comparing-fractions-mt_IfEgu0X449)

## Opens up

- [Probabilities Sum to One](https://lightmysky.com/learn/mathematics/probabilities-sum-to-one-mt_3fwYu7imd4)
- [Calculating Simple Probability](https://lightmysky.com/learn/mathematics/calculating-simple-probability-mt_Zt30Gxi-qp)