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0.5USING

PROBABILITY FORMULAS

AND WORKING

BACKWARDS

Substitute in the information you have in to the appropriate formula.

Solve for the missing piece.

Use your algebra skills.

Working with Formulas

Mutually ExclusiveP(A B) = P(A) + P(B)

IndependentP(A B) = P(A) P(B)

OverlappingP(A B) = P(A) + P(B) – P(A B)

DependentP(A B) = P(A) P(B|A)

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The probability of Sam getting an A on the Chemistry test is 0.76. The probability of him getting an A on his Calculus test and an A on his Chemistry test is 0.494. What is the probability of him getting an A on his Calculus test given that he got an A on his Chemistry test?

Example 1 – Dependent

P(A B) = P(A) P(B|A)

0.494 = 0.76 P(B|A) 0.65 = P(B|A)

An optional camp to improve players’ basketball skills was held in the county. The probability of a kid attending was 0.62. The probability that they attended and made the honor roll was 0.44. What is the probability that they made the honor roll?

Example 2 – Independent

P(A B) = P(A) P(B)

0.44 = 0.62 P(B)

0.71 = P(B)

P(A) = ¼P(B) = 5/8P(A B) = ¾

Find P(A B)

Example 3 – Overlapping (Inclusive)

P(A B) = P(A) + P(B) – P(A B)

1/8 = P(A B)

3 1 5P A B

4 4 8

6 P

rob

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sWorksheet

Using Probability Formulas and

Working Backwards