Probability

Students learn how to measure the likelihood of an event happening using keywords, fractions, decimals and percentages.  Learning progresses on to calculating a relative frequency and using tree diagrams to find the probability of two or more events.

This unit takes place in  and follows on from working with fractions and mixed numbers.


Probability Lessons 


Prerequisite Knowledge
  • compare and order fractions whose denominators are all multiples of the same number
  • identify, name and write equivalent fractions of a given fraction, represented visually, including tenths and hundredths
  • add and subtract fractions with the same denominator and denominators that are multiples of the same number

Success Criteria
  • record describe and analyse the frequency of outcomes of probability experiments using tables and frequency trees
  • apply ideas of randomness, fairness and equally likely events to calculate expected outcomes of multiple future experiments
  • relate relative expected frequencies to theoretical probability, using appropriate language and the 0 – 1 probability scale
  • apply the property that the probabilities of an exhaustive set of outcomes sum to one; apply the property that the probabilities of an exhaustive set of mutually exclusive events sum to one
  • understand that empirical unbiased samples tend towards theoretical probability distributions, with increasing sample size
  • enumerate sets and combinations of sets systematically, using tables, grids, Venn diagrams and tree diagrams
  • construct theoretical possibility spaces for single and combined experiments with equally likely outcomes and use these to calculate theoretical probabilities
  • calculate the probability of independent and dependent combined events, including using tree diagrams and other representations, and know the underlying assumptions


Key Concepts
  • Use the probability scale and associated keywords to begin comparing the likelihood of an event’s occurrence.
  • When writing probabilities as a fraction using the probability scale to show equivalences with the keywords
  • Discuss the effect of bias and sample size when comparing theoretical and experimental probabilities.
  • Use the random function on a calculator or spreadsheet to demonstrate simple randomisation.
  • When listing the outcomes of combined events ensure students use a logical and systematic method.
  • Branches on a probability tree have a sum of one as they are mutually exclusive.

Common Misconceptions
  • Writing probabilities as a ratio is a common misconception.
  • When creating Venn diagrams students often forget to place the remaining events outside the circles.
  • When listing permutations of combined events students often repeat events when they do not use a logical and systematic method.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Mr Mathematics Blog

Mathematics OFSTED Inspection – The Deep Dive

Earlier this week, my school took part in a trial OFSTED inspection as part of getting ready for the new inspection framework in September 2019. This involved three Lead Inspectors visiting our school over the course of two days. The first day involved a ‘deep dive’ by each of the Lead Inspectors into Mathematics, English […]

How to Solve Quadratics by Factorising

The method of how to solve quadratics by factorising is now part of the foundational knowledge students aiming for higher exam grades are expected to have.   Here is an example of such a question. Solve x2 + 7x – 18 = 0 In my experience of teaching and marking exam papers students often struggle with […]

How Write 3 Part Ratios

When learning how to write 3-part ratios students need to understand how ratios can be made equivalent. The start of the lesson reminds students by asking which of six ratios is the odd one out.  This is presented to the class as they come into the lesson.    Writing Equivalent Ratios  A few students immediately go […]