Class 12 Maths Probability Conditional Probability Problems

Conditional Probability Problems:


Example: In a survey in a class it was found that the probability of a student watching Examfear videos is 0.8. and the probability that a student is both topper and also watches Examfear videos is 0.792. what is the probability that a student is a topper if he watches Examfear videos?


Solution:
Let E denotes the event that a person watches Examfear videos 
Let F denotes the event that a person is topper . Then,
P(E) =The probability that a person watches Examfear videos =0.8
P(E∩F)=probability that one is both topper and also watches Examfear videos = 0.792
and P(F|E)= the probability that a person is a topper if he watches Examfear
videos=?
then according to Formula for conditional probability
P(F|E) = P(F∩E)/ P(E)
= 0.792/0.8
= 0.99
∴ The probability that a person is a topper if he watches Examfear videos is
0.99

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