Frequency Trees Flashcards

All 5 cards in this deck

What is a frequency tree?

A diagram whose branches split a total into groups, with the frequency (a whole number) written at the end of each branch.

True or false? The numbers written on a frequency tree are probabilities.

False. They are frequencies — whole numbers of items or people.

In a frequency tree, what must be true of the frequencies on the branches coming out of one point?

They add up to the frequency at that point.

e.g. a group of $60$ splitting into $15$ and $45$.

What are the steps to complete a frequency tree?

e.g. $100$ people take a test: $60$ are men, $15$ of the men passed, $40$ people passed altogether

1. Write the total and the first split: $60$ men, $100 - 60 = 40$ women.
2. Complete a split using its own group total: men who failed $= 60 - 15 = 45$.
3. Use the overall totals for the rest: women who passed $= 40 - 15 = 25$, women who failed $= 40 - 25 = 15$.

How do you find a probability from a completed frequency tree?

e.g. P(a person chosen at random passed the test)

Add the end frequencies for that outcome and divide by the total at the start of the tree.

e.g. $\frac{15 + 25}{100} = \frac{40}{100}$.