Flashcards · Maths · Probability
Frequency Trees and Two-Way Tables
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What is a two-way table?
A table that sorts data by two features at once, with totals for rows and columns.
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What do the numbers in each row of a two-way table add up to?
The total at the end of the row.
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How do you find a missing number in a two-way table?
Subtract the known numbers from the row or column total.
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What is the grand total in a two-way table?
The total of all the items, in the bottom right corner.
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What is a frequency tree?
A tree diagram that shows numbers of items rather than probabilities.
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What should a pair of branches in a frequency tree add up to?
The number they came from.
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What is 60% of 200?
120.
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How do you find the probability from a two-way table?
The number in the cell, or cells, divided by the grand total.
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How do you estimate the expected number from a probability?
Multiply the probability by the number in the group.
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13 of 100 students cycle. How many of 500 would you expect to cycle?
\(\dfrac{13}{100} \times 500 = 65\).
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24 of 100 pupils are girls who walk. What is the probability?
\(\dfrac{24}{100} = \dfrac{6}{25}\).
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How can you check that a two-way table is complete?
The row totals and the column totals should both add to the grand total.
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If 22 of 50 people own a cat only and 14 own a dog only, with 6 owning both, how many have neither?
\(50 - 42 = 8\).
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Why must you check which row or column a number is in?
Numbers in the wrong row give wrong totals and wrong probabilities.
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What is 25% of 120?
30.
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Why draw a table or a tree for a wordy problem?
It organises the information and shows which numbers are missing.