SOLUTION: In a class of 40 people the probability of meeting a student of at least 13 years old is 0.8. Calculate the numbers of students in class who are expected to be less than 13 years

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Question 985628: In a class of 40 people the probability of meeting a student of at least 13 years old is 0.8. Calculate the numbers of students in class who are expected to be less than 13 years
Answer by mathmate(429) About Me  (Show Source):
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Given:
A class of 40 students.
Probability of a student being >= years old = 0.8

Solution:
number of students, n = 40
probability of a student being not >=13 years old, p
= probability of a student being < 13 years old = 1-0.8 = 0.2
Expected value = np = 40 * 0.2 = 8

Answer: Eight students are expected to be under 13.