Conditional Probability

                      Lesson 1

Problem:                   What is the probability of choosing O or H from letters of word ORTHOGRAPHIC?

Step 1:  Probability of choosing O, P (A) = 2/12

Solution Probability of choosing H, P (B) = 2/12

                                                             Step 2:                                  

Solution Probability of choosing O or H = P (A) + P (B) – P (A and B)

                                                             Step 3:      

= 2/12 + 2/12 – 0

= 4/12

 Step 4:                     The answer is:  1/3

 Complete   

                                                            Try two practice problems:  

A.	The probability that it is Friday and that a student is absent is 0.03. Since there are 5 school days in a week, the probability that it is Friday is 0.2. What is the probability that a student is absent given that today is Friday?
B.	At Kennedy Middle School, the probability that a student takes Technology and Spanish is 0.087. The probability that a student takes Technology is 0.68. What is the probability that a student takes Spanish given that the student is taking Technology?

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