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.
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