Handling Data 5
2 marks · HardThe table shows the probability that each branch is followed on a probability tree diagram. | First Event | Probability | |:-----------:|:----------:| | Heads | 0.4 | | Tails | 0.6 |
What does the sum of the probabilities on the branches from any single event add up to in a tree diagram? Explain briefly.
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The sum of the probabilities on branches from a single event in a probability tree diagram is 1.
Also accept: All branches from a single event add up to 1.; The total probability from one event is 1.
Common mistakes: Saying the sum is less than or greater than 1; Ignoring that branches cover all possible outcomes
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that the sum of branch probabilities from a single event is 1.
B2 · 1 mark · Provides a brief, correct explanation (e.g. 'all possible outcomes must add to 1').
Worked solution
In a probability tree diagram, the sum of the probabilities on the branches from a single event must add up to 1. This is because the branches show all possible outcomes from that event, and the total probability for all possible outcomes is always 1.