AI generatedProbabilityKS3 / GCSE

Probability from a frequency tree

Probability from a frequency tree.

  • A frequency tree records counts, not probabilities.
  • The counts leaving a branch point add to the count arriving there.
  • For a probability, divide the relevant final count by the correct total.

Example 1

A pupil is chosen at random from these 24 pupils. Find .

Frequency tree for 24 pupilsTravelClubWalk12Yes8No4Bus12Yes7No5
Club totalAdd disjoint end groups.
Use the total number of pupils.

Example 2

A pupil is chosen at random from these 26 pupils. Find .

Frequency tree for 26 pupilsTravelClubWalk13Yes9No4Bus13Yes8No5
Club totalAdd disjoint end groups.
Use the total number of pupils.

Your turn

Question 1

A pupil is chosen at random from these 28 pupils. Find .

Frequency tree for 28 pupilsTravelClubWalk14Yes10No4Bus14Yes9No5
Check answer
Club totalAdd disjoint end groups.
Use the total number of pupils.
Question 2

A pupil is chosen at random from these 31 pupils. Find .

Frequency tree for 31 pupilsTravelClubWalk16Yes11No5Bus15Yes10No5
Check answer
Club totalAdd disjoint end groups.
Use the total number of pupils.
Question 3

A pupil is chosen at random from these 33 pupils. Find .

Frequency tree for 33 pupilsTravelClubWalk17Yes12No5Bus16Yes11No5
Check answer
Club totalAdd disjoint end groups.
Use the total number of pupils.
Question 4

A pupil is chosen at random from these 36 pupils. Find .

Frequency tree for 36 pupilsTravelClubWalk18Yes13No5Bus18Yes12No6
Check answer
Club totalAdd disjoint end groups.
Use the total number of pupils.
Question 5

A pupil is chosen at random from these 39 pupils. Find .

Frequency tree for 39 pupilsTravelClubWalk20Yes14No6Bus19Yes13No6
Check answer
Club totalAdd disjoint end groups.
Use the total number of pupils.
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