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1.9 Probability. Two Steps for Probability Problems. Determine all possibilities in a logical manner. Count them Determine the number of these possibilities that are “favorable”. Sometimes they are called “winners”. Probability = (Number of Winners)/(Number of Possibilities). Sample Problems.
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Two Steps for Probability Problems • Determine all possibilities in a logical manner. Count them • Determine the number of these possibilities that are “favorable”. Sometimes they are called “winners”. • Probability = (Number of Winners)/(Number of Possibilities)
Sample Problems If one of the four points is picked at random, what is the probability that the point lies on the angle? Answer: Possible points = 4 Winners = 4 P/W=4/4=1=100% A B C D
More Problems… If two of the four points are selected at random, what is the probability that both lie on ray CA? List all possibilities – AC, AB, AD, BC, BD, CD List winners – AC, AB, BC W/P = 3/6 = 1/2 A B C D
And Again… If three of the four points are selected in a random order, what is the probability that the ordered letters will correctly name the angle shown? Answer: Done in Class 1/6 A B C D
A point Q is randomly chosen on AB. What is the probability that it is within 5 units of C? Answer: Look at regions Possible Region = 12 units (15-3) Winning Region = 9 units (5 to the left and 4 to the right) W/P = 9/12 = 3/4 A C B 11 15 3