Probability · Basic probability
Chapter 1 · 3
The idea
Frequency trees
A frequency tree sorts one group by two questions, and every box is a count that splits into the boxes after it. How to complete a tree from facts in words (counts, fractions, percentages or a ratio), work backwards from a partly filled tree, turn it into a two-way table, and read off fractions and probabilities with the right group on the bottom.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
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Probability · Basic probability
Frequency trees
A frequency tree sorts one group by two questions, and every box is a count that splits into the boxes after it. How to complete a tree from facts in words (counts, fractions, percentages or a ratio), work backwards from a partly filled tree, turn it into a two-way table, and read off fractions and probabilities with the right group on the bottom.
Why it works
A frequency tree sorts one group twice
One morning, Year 9 students arrive at school: walk and come by bus. of the bus students are late, but only of the walkers. So is the bus the worse way to get to school? A frequency tree lays the numbers out so you can answer that.A frequency tree sorts one group by two questions, one after the other. The first box holds everyone. Its branches split them by how they travelled. Each of those boxes splits again, by whether they were late. Every number in a box is a count of students.
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The rest of the explanation, plus 4 worked examples you step through move by move.
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