True or False? The sum of all probabilities is 1 .

True. As long as the possibilities considered are all mutually exclusive (non-overlapping), then the sum of all probabilities is 1 .

GCSEMathsEdexcelFoundationFlashcardsProbabilityTree Diagrams & Combined Probability

Tree Diagrams & Combined Probability (Edexcel GCSE Maths: Foundation): Flashcards

Exam code: 1MA1

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What does AND mean for combined probabilities?
AND means multiply ( $\times$ ) and is used for independent events to find the probability of both events occurring.
E.g. the probability of events A and B occurring is $P (A) \times P (B)$ .
What does OR mean for combined probabilities?
OR means add (+) and is used for mutually exclusive events to find the probability of one event or the other event occurring.
E.g. the probability of either event A and/or event B occurring is $P (A) + P (B)$ .
True or False?
The sum of all probabilities is 1.
True.
As long as the possibilities considered are all mutually exclusive (non-overlapping), then the sum of all probabilities is 1.
State the equation for the probability of two independent events, $A$ and $B$ , occurring together.
If $A$ and $B$ are independent events, then the probability of both events occurring is:
$P (A and B) = P (A) \times P (B)$ .
State the equation for the probability of one or the other of two mutually exclusive events, $A$ and $B$ , occurring.
If $A$ and $B$ are mutually exclusive events, then the probability of one or the other of them occurring is:
$P (A or B) = P (A) + P (B)$ .

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