© 2004  Rasmus ehf

Probability

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Lesson 3

If  3 coins are tossed, what is the probability of 'heads' facing up on all the coins?

Example 1

Use a probability tree:

The probability of getting 'heads' on 3 coins:

 . 

You can find the answer by following the branches marked H-H-H (shown in red on the diagram).       

Example 2

Here are two bags with different coloured marbles.

If you take  one marble from each bag (without looking), what is the probability that both the marbles will be blue?

Look at part of a probability tree.

Example 3

  Here is a bowl of red and green sweets.

If you take one sweet from the bowl (without looking ) and eat it and then take another, what is the probability that they will both be red?

Use a probability tree:

Here are the possible outcomes:

Red - Red:
Green - Green:
Mixed colors:

Practice these methods and then take Quiz 3 on Probability. Remember to use the Checklist to keep track of your work.