E5

=//**E5. Multiplication Rule for probability.**// =

Need to know - P(A and B) = P(A) * P(B|A)

Example problem -

Seventy percent of students getting an DS, AD, or CO in math 2/3 study at least six hours a week. Forty-five percent of students in math 2/3 who study at least six hours a week belong to a study group. Find the probability that an math 2/3 students who gets an DS, AD, or CO studies at least six hours a week and belongs to a study group.

How to find the probability.

A= study at least 6 hr/week

P(A) = .70

B = belong to a study group

P (B|A) = .45

P(A and B) = .7 * .45 = .315

Common mistakes -

Forgetting the “and” or what it means. When a problem asks you to find A and B, you must remember its for both.

Good websites to go and help you out-

http://stattrek.com/Lesson1/ProbabilityRules.aspx