Edexcel IGCSE Math A 6.3.I Addition Rule for Mutually Exclusive Events

Practise adding probabilities of mutually exclusive outcomes and recovering missing category probabilities from a total of one.

Exam points

verify the outcomes cannot occur together before adding their probabilities
add the required mutually exclusive category probabilities for an either-or event
subtract known categories from 1 before combining an outcome with a missing category

[Maximum number: 1]

Here is a biased spinner.

When the spinner is spun once, the probabilities that it lands on red or on yellow or on green are given in the table.

Work out the probability that the spinner lands on red or on yellow.

0.45

1

B1 oe eg $\frac{9}{20}, \frac{45}{100}, 45 \%$

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