SOLUTION: Certain class contains 60% of boys and 40% of girls, all aged between 17 and 27 years. It is known that 80% of young people of both sexes are under 21 years of age and that among g

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Question 1105388: Certain class contains 60% of boys and 40% of girls, all aged between 17 and 27 years. It is known that 80% of young people of both sexes are under 21 years of age and that among girls, 10% are over 21 years.

a) a person is chosen and it is verified that he is under 21 years. What is the probability of being a girl?
b) a person is chosen at random. What is the probability of being a boy under the age of 21?
c) choose a boy at random. How likely is he to be less than 21 years old?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
Use 1000.
=====B===========G========total
<21--- 440----------360========800
>21----160------------40========200
Total--600-----------400---------1000
a. <21 is 0.45 probability of being a girl.
b. 0.44 probability of being a boy under 21
c. Boy less than 21 is 0.73 probability, given that a boy is chosen.