# Lesson 10.9 AIM: The and and or Rules of Probability.

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Lesson 10.9 AIM: The and and or Rules of Probability

DO NOW CRAYON has 6 letters. 6 x 5 x 4 x 3 x 2 x 1 = 720 ways

The and rule… When you want to find P(event 1) AND P(event 2) you multiply.

The or rule… When you want to find P(event 1) OR P(event 2) you add.

What is the probability that Brianna will move fewer than four spaces? What is the probability that she will move backwards? To find the probability of both happening (and) you multiply the probabilities.

What is the probability that Mr. Yee will choose a girl first? What is the probability that Mr. Yee will choose a girl second? To find the probability of both happening (and) you multiply the probabilities.

What is the probability that you will roll a prime number? What is the probability that the number is divisible by 2? To find the probability of either happening (or) you add the probabilities. What is the probability that you will roll a number that is prime and divisible by 2?

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