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Probability - 7 students

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Probability - 7 students

by ramyaravindran » Sun Jan 17, 2010 12:43 pm
In a class of 20 students, one half of the students are boys, if a teacher has to select 7 students and the first 6 are girls.What is the probability that the 7th student is a girl

The given answer is [spoiler]2/7[/spoiler]

Can somebody explain how to solve this question?Thanks.[/spoiler]
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by bln123 » Sun Jan 17, 2010 2:11 pm
[spoiler]20 Students, 10 male, 10 female

6 are already picked, all girls -> remaining students: 4 female, 10 male

probability of 7th pick being female: 4 (number of females remaining) / 14 (number of all students remaining)

4/14 -> 2/7 (-> around 28%)[/spoiler]
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