McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
6. Probabilities of Mutually Exclusive Events
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Exercise 19 Page 930

The sum of the probability of an event and the probability of its complement is 1.

7/8 or about 87.5 %

Practice makes perfect

We are told that a spinner numbered 1 to 8 is spun.

Recall that the experimental probability of an event measures the likelihood that the event occurs based on the actual results of an experiment. P(Event)= Number of times the event occurs/Number of times the experiment is done

We want to find the probability of not landing on 5. Note that this is the complement of spinner landing on 5. The sum of the probability of an event and the probability of its complement is 1. P(Event)+P(Not event)=1 Let's start by finding the probability of a spinner landing on a 5, which will be our event. The number of times the experiment is done is the total number of parts on the spinner, 8. The number of times the event occurs is the number of parts of the spinner numbered 5.

There is 1 part numbered 5 on the spinner. Now, we can write P(5). P( 5)=1/8 l← ← lPart number5 Total parts The experimental probability of landing on part 5 is 18. Let's now find the probability of its complement, which is landing on a part that is not numbered 5.
P(5)+P(Not5)=1
1/8+P(Not5)=1
Solve for P(Not5)
P(Not5)=1-1/8
P(Not5)=8/8-1/8
P(Not5)=7/8
Convert to percent
P(Not5)=0.875
P(Not5)=87.5 %
We found that P(Not5) is 18, whhich can be also written as 87.5 %.