Teach Genie
Teach it back in your own words, spot gaps, and remember it better.
A probability tree shows events happening in stages. Each split represents the possible outcomes of one event.
At any split, the branch probabilities must add to 1. If one branch is missing, use the complement rule P(not A)=1−P(A)P(\text{not }A)=1-P(A)P(not A)=1−P(A).
A split can have two branches or three, such as win, draw, lose, but the labels from one point still add to 1. Then read the question language carefully: multiply along a route for both, and add route totals when the event can happen in more than one way.
Question 1
4 marksTina has two bags of counters, Bag A and Bag B.
There are 5 red counters and 3 blue counters in bag A.
There are 4 red counters and 5 blue counters in bag B.
Tina takes at random a counter from each bag.
If P(win)=0.65P(\text{win}) = 0.65P(win)=0.65, what probability is assigned to the complement branch?
Revision notes for Edexcel GCSE Maths Probability Trees. Open the guide for explanations and worked examples. Written against the Edexcel GCSE Maths (1MA1) specification, so the content matches what's examinable rather than general Maths background.
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A player wins a game with probability 0.680.680.68. What probability should go on the “not win” branch of a probability tree?
