We call a number a descending number if each digit is strictly smaller than the digit that comes before it.  For example, 863 is a descending number.  How many 3-digit descending numbers are there?
Question:
We call a number a descending number if each digit is strictly smaller than the digit that comes before it.  For example, 863 is a descending number.  How many 3-digit descending numbers are there?
Answer:
Let's think step by step.

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We call a number a descending number if each digit is strictly smaller than the digit that comes before it.  For example, 863 is a descending number.  How many 3-digit descending numbers are there?
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