Probability
Probability reference sheet
A printable guide to probability, independent and dependent events, replacement and probability trees. Connect definitions with worked examples and conditional branch probabilities.
Preview and downloadProbability practice
Probability with numbers worksheets
Find the chance of selecting a number from a finite set. Practice ranges up to 10, 25 or 50, count favorable outcomes and simplify the probability with an explained answer key.
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Read the range and event carefully. Count the numbers that satisfy the condition, divide by the number of equally likely outcomes, and simplify.
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Customize this worksheetCount the outcomes that match the event
Each question makes its experiment and event explicit. The answer key connects the favorable count with the whole sample space, then simplifies the fraction. Selected question families control what appears on the sheet.
A probability is a property of the stated model. When outcomes are not equally likely, a simple count of different labels is not enough. With two dice, use 36 ordered pairs rather than eleven possible sums.
Learning objective
What this activity builds
Describe an event as a set of matching numbers and compare its size with the full sample space.
Worked example
One integer from 1 through 10 is chosen at random, each with the same chance. What is the probability of an even number?
5/10 = 1/2.
The favorable outcomes are 2, 4, 6, 8 and 10. There are five matching numbers among ten possible choices. Both endpoints belong to the stated range.
Teaching notes
Make the practice count
- List the sample space before calculating a fraction.
- Use numbered cards to model equal chances.
- Ask learners to justify which endpoints belong to an event.
- Compare an event with its complement; their probabilities add to 1.
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A useful next step
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