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# Probability as fractions, decimals or percentages
- URL: https://www.esheets.io/probability-as-fractions-decimals-or-percentages/
- Published: 2025-06-14T20:28:31.000Z
- Updated: 2026-06-21T18:32:21.000Z
- Author: Richard Linnington
- Tags: Maths, Probability

Probability helps us measure how likely something is to happen—whether it's winning a game, catching the bus on time, or flipping heads on a coin. We can express these chances as fractions, decimals, or percentages, depending on the situation. Understanding all three forms helps you interpret real-world risks and make better decisions. [Jump to the questions](#practise-now)

## Practise now

Worksheet preview and key skills 

### Worksheet preview

Practise probability as fractions, decimals or percentages with this self-marking maths worksheet.

The interactive worksheet below generates questions, gives instant feedback, and lets students record their score.

#### What you’ll practise

- Writing probability as a fraction, decimal or percentage.
- Recognising that probabilities are between 0 and 1.
- Converting between probability formats.
- Interpreting probability values correctly.

Use the interactive worksheet below, or read the [Topic guide](#topic-guide) for the method and worked example.

Calculate the probability of picking the specified counter. Format your answers as requested. 

## Topic guide

### What this worksheet practises

This worksheet provides practice on calculating simple probabilities and writing the answers correctly. A probability describes how likely an event is to happen. It can be written as a fraction, a decimal, or a percentage, but all probabilities must lie between 0 (impossible) and 1 (certain).

### Key method

Fractions are usually the easiest way to write a probability.

- Count the total number of possible outcomes. This number goes on the **bottom** of your fraction (the denominator).
- Count the number of "successful" outcomes (the things you actually want to happen). This number goes on the **top** of your fraction (the numerator).
- If the question asks for a decimal or percentage, convert your fraction at the end.

### Worked example

**A bag contains 3 red balls, 5 blue balls, and 2 green balls. A ball is chosen at random. What is the probability of picking a blue ball?**

Step 1: Find the total number of balls.

3 + 5 + 2 = 10 balls total. Our denominator is 10.

Step 2: Find the number of successful outcomes.

There are 5 blue balls. Our numerator is 5.

Step 3: Write the probability.

As a fraction: 5/10 (which simplifies to 1/2).

As a decimal: 0.5

As a percentage: 50%

### Common mistakes to avoid

The single most common mistake is writing a probability as a ratio. For example, writing the probability of picking a blue ball as "5:5" (5 blue to 5 non-blue). **Never** write a probability as a ratio with a colon. It will be marked wrong in any exam. Always use a fraction.

### Things to remember

The probability of an event happening, plus the probability of it *not* happening, must always add up to exactly 1 (or 100%). If the probability of rain is 0.2, the probability of it *not* raining is 0.8.