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One day while you're speaking to two boys of the same family, they tell you:
"I have a brother two years older than me."
"I have a brother three years older than me."
The next day, two boys from the same family tell you:
"I have a brother one year younger than me."
"I have a brother four years younger than me."
What is the minimum number of sons there could possibly be in that family?
Three brothers is correct!
The key to this puzzle is that the second conversation happened on the next day.
If it was the middle brother's birthday on the second day, the brothers' age differences would have changed as shown in the diagram above.
Actually, this can also work when it's either the youngest or oldest brother's birthday. Can you see how?
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