Edexcel IGCSE Math B 10.J simple conditional probability

Practise simple conditional probability by restricting the total to the given group, then counting the outcomes that also meet the second condition.

Exam points

Use the given condition to choose the correct reduced total for the probability.
Find the overlap within that group, such as vanilla and chocolate or hockey and rugby.

[Maximum number: 2]

Figure for Question 10.J Simple conditional probability question 1 — Edexcel IGCSE Math B

$\mathscr E=\{2,3,4,5,6,7,8,9,10\}$ $P=\{\text{prime numbers}\}$ $E=\{\text{even numbers}\}$ $F=\{\text{factors of }36\}$

70 children were asked which flavours of ice cream they like from chocolate (C), vanilla (V) and strawberry (S).
5 children like chocolate and vanilla and strawberry.
15 like strawberry only.
12 like chocolate only.
8 like none of the flavours.
6 like strawberry and vanilla.
11 like chocolate and vanilla.
21 like strawberry.
35 like vanilla.

One of the 70 children is chosen at random.
Given that this child likes vanilla, find the probability that this child also likes chocolate.

Final answer:
$\frac{11}{35}$

B2 for $\frac{11}{35}$ or equivalent, e.g. $0.31\ldots$ rounded/truncated to 2 significant figures.

B1ft for $\frac{11}{a}$ , where a>11 and a=6+5+23+1, or $\frac{b}{35}$ , where b<35 and b=6+5, or 11:35.

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10.J Simple conditional probability question 1