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Edexcel IGCSE Maths (4MA1) · Unit 6: Statistics & Probability

IGCSE Maths Tree Diagrams and Conditional Probability Questions and Answers

Tree Diagrams and Conditional Probability questions with full solutions for Pearson Edexcel International GCSE Mathematics A (4MA1), Higher tier. Read the 3 worked examples first, then cover each solution and redo it yourself.

Practise tree diagrams and conditional probability in Unit 6 →Tree Diagrams and Conditional Probability revision notes

What this topic covers

Tree Diagrams and Conditional Probability worked examples

Worked example 1: Tree diagram with independent events

The probability of passing a test is 0.7. Two independent tests are taken. Find P(passing exactly one).

Solution

  1. Pass then fail: \(0.7\times0.3=0.21\).
  2. Fail then pass: \(0.3\times0.7=0.21\).
  3. Total \(0.42\).

Answer: 0.42

Tip: Multiply along branches, add between outcomes.

Worked example 2: Without replacement

A bag has 3 red and 7 blue balls. Two are taken without replacement. Find P(both blue).

Solution

  1. First blue: \(\tfrac{7}{10}\).
  2. Second blue: \(\tfrac{6}{9}\) (one blue has gone).
  3. \(\tfrac{7}{10}\times\tfrac{6}{9}=\tfrac{7}{15}\).

Answer: \(\tfrac{7}{15}\)

Tip: Both the numerator and denominator change on the second pick.

Worked example 3: Conditional probability from a table

Of 25 adults, 18 like tea; of 15 children, 9 like tea. A tea drinker is chosen at random. Find P(adult).

Solution

  1. Tea drinkers: \(18+9=27\).
  2. \(P(\text{adult}\mid\text{tea})=\dfrac{18}{27}=\dfrac{2}{3}\).

Answer: \(\tfrac{2}{3}\)

Tip: 'Given' restricts you to one row or column.

Every question and worked example here is original, written for IGCSE Math Revision rather than copied from Pearson papers, and each answer was re-solved independently before publishing.

Revise tree diagrams and conditional probability for the exam

Questions students ask

Which Edexcel IGCSE Maths papers test tree diagrams and conditional probability?

Either Higher tier paper, 1H or 2H, can test tree diagrams and conditional probability: both cover the whole Pearson Edexcel International GCSE Mathematics A (4MA1) specification and both allow a calculator. Show your method, because most marks are for working.

Where can I practise more tree diagrams and conditional probability questions?

In the IGCSE student hub: Unit 6 (Statistics & Probability) has more exam-style questions on this topic, each with a mark scheme. Practice starts with a 7-day free trial; the worked examples and questions on this page are free.

More Unit 6 topics: Statistics & Probability