Unit 2 & Unit 3 · Both
Statistics & Probability
Averages, charts, probability (including tree diagrams) and statistical diagrams.
Probability is a major focus of the non-calculator unit. Work confidently with theoretical probability, relative frequency and tree diagrams.
Practice lesson for the WJEC Mathematics and Numeracy Double Award. This is not an official WJEC page.
Basic probability
P(event) = favourable outcomes / total possible outcomes
Probabilities are between 0 and 1.
P(not A) = 1 − P(A)
Tree diagrams
Used for combined events (with or without replacement).
• Multiply along branches for a combined outcome
• Add probabilities of different routes that give the same result
Worked example
Bag: 5 red, 3 blue. Two taken without replacement. P(both red)?
Solution
(5/8) × (4/7) = 20/56 = **5/14**
Averages
• Mean = total ÷ number of values
• Median = middle value when ordered
• Mode = most frequent value
• Range = highest − lowest
Practice questions
Try these without looking at the answers first.
Q1.Bag: 4 green, 6 yellow. One taken at random. P(green)?
Show answer
2/5 or 0.4
Q2.Same bag, two without replacement. P(both yellow)?
Hint: (6/10)×(5/9)=30/90=1/3
Show answer
1/3