Probability Trees
Teach Genie
Review Probability Trees by teaching 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?
Probability Trees Revision Guide
Revision notes for WJEC GCSE Maths Probability Trees: explanations and worked examples.