Problem 1 · 2018 Math Kangaroo
Medium
Logic & Word Problems
casework
Every child in my family has at least two brothers and at least one sister. What is the minimum number of children in my family?
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Answer: C — 5
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Hint 1 of 2
Count the boys first, then ask what each girl still needs.
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Hint 2 of 2
A boy needs two other boys (so at least three boys); a girl needs one other girl (so at least two girls).
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Approach: set the minimum each gender forces
- Each child has at least 2 brothers, so there must be at least 3 boys (every boy needs two other boys).
- Each child has at least 1 sister, so there must be at least 2 girls (every girl needs one other girl).
- Three boys and two girls satisfies both conditions for everyone.
- So the minimum is 5 children.
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