W.c.1Feb.GCSE.End.of.lesson.Quiz.Probability2

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Two events are independent if they have an effect on each other.

• False

• True

Two events are dependent if they have no effect on each other.

• True

• False

Is this Probabilty tree showing an independent or dependent event?

• dependent

• independent

If I eat one green jelly baby, which tree diagram shows the correct probabilities for the second jelly baby ?

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What is the probability of eating 1 green and then 1 red jelly baby?

•  $\frac{3}{10}\times\frac{5}{9}=\frac{15}{90}=\frac{1}{6}$  

•  $\frac{5}{10}\times\frac{2}{9}=\frac{10}{90}=\frac{1}{9}$  

Which tree diagram shows the correct completed tree diagram?

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Answer explanation

What's the probability that two red balls are picked?

• $\frac{3}{10}+\ \frac{7}{9}=\frac{10}{19}$

• $\frac{3}{10}\times\frac{3}{9}=\frac{9}{90}=\frac{1}{10}$

• $\frac{3}{10}\times\frac{2}{9}=\frac{5}{90}=\frac{1}{18}$

• $\frac{3}{10}+\frac{2}{9}=\frac{5}{19}$

Answer explanation

To find the probability of a combination of outcomes, multiply the probabilities along the relevant branches. If more than one combination gives the desired outcome, add their probabilities

Eg a bag contains 3 red and 7 blue balls.

A ball is picked, not replaced, and another picked.

Find the probability that:

a)1 of each colour is picked

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Answer explanation

To find the probability of a combination of outcomes, multiply the probabilities along the relevant branches. If more than one combination gives the desired outcome, add their probabilities