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Junior Mathematical Olympiad

Combinatorics Difficulty 1.6 Junior Find the answer Netherlands

How many three-digit numbers, with each digit unequal to zero, are there such that the three digits add up to $7$ ?
A) $4$ B) $7$ C) $10$ D) $15$ E) $21$

This was a multiple-choice question, but the options didn't survive into the source we have. The answer given is D, and the solution below works it through.

Solution

D) $15$

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Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.