In a classroom, there are 50 students, including boys and girls. At least one of the students is a boy. Taking any pair of students, at least one of the two is a girl. How many girls are there in this classroom?

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Solution

Since there is at least one boy, let João be the boy in the class. For each pair formed with João, at least one is a girl, that is, any student who pairs with João will be a girl. Therefore, there are 49 girls in this class.

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