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 16 Page 930

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

25/36 or about 69.4 %

Practice makes perfect

We are told that a pair of dice is rolled.

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 getting a 3 on a pair of dice. Note that this is the complement of getting a 3. 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 rolling a 3, which will be our event. Now, we can calculate the number of outcomes for a pair of dice knowing that each die has 6 different outcomes. 6*6= 36 ← Total outcomes There are 36 outcomes, which is also the number of times the experiment is done. The number of times the event occurs is the number of different outcomes that result in getting at least one 3 on a pair of dice.

There are 11 such outcomes. Now, we can write P(3). P( 3)=11/36 l← ← lAt least one3 Total outcomes The experimental probability of getting a 3 is equal to 1136. Let's now find the probability of its complement, which is not getting a 3 on a pair of dice.
P(3)+P(Not3)=1
11/36+P(Not3)=1
Solve for P(Not3)
P(Not3)=1-11/36
P(Not3)=36/36-11/36
P(Not3)=25/36
Convert to percent
P(Not3)=0.694
P(Not3)≈0.694
P(Not3)≈69.4 %
We found that P(Not3) is 2536 or about 69.4 %.