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1. Dialogue

Mike: Hey, Min-su! Let me show you something.

Min-su: OK. What is it?

Mike: Write down three numbers in a row.

Min-su: Go ahead. I'm ready.

Mike: Write down the same three numbers backwards. Subtract the smaller number from the bigger number.

Min-su: OK. I did.

Mike: The answer is 198.

Min-su: Wow. How amazing! How did you know?

Mike: It's a secret.