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Probability

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Lesson 2

Repeated probability experiments:

When you toss a coin there are two possible outcomes: 'heads' or 'tails'. Each of these outcomes is equally likely, since there is 1 'head' and 1 'tail' on the coin.

The sum of the possible outcomes is always = 100%

Example 1

If a coin is tossed twice, what is the probability of 'heads' coming up both times?

A tree diagram is one way of showing all the possible outcomes.  

To calculate the probability of getting 'heads' in both throws
multiply the possible outcomes

The result is the probability of getting 'heads' twice in a row. 

Other possible outcomes are calculated in the same way.

The sum of the possible outcomes:

You can find the probability of getting 'heads' in one toss and 'tails' in the other by adding the probabilities:    

(H and T) =

+ (T and H) =

or

Example 2

Stefan was fouled in a basketball game and was awarded two penalty shots. His average for scoring on penalties is 70%. What is the probability that he will score on both shots?

A probability tree can be used to find the answer.      

The probabilty is		or		The probabilty is		or
that he will make a basket twice in a row.				that he will not make a basket twice in a row.

 To check to see if the calculation is correct, you can add the sum of the possible outcomes after the second try:  

Practice these methods and then take Quiz 2 on Probability. Remember to use the Checklist to keep track of your work.