How many integers from to , inclusive, have digits that add up to ?
Answer and explanation
Correct answer: B.
- Step 1: Let the three digits be such that with and .
- Step 2: Substitute , transforming the relation to for non-negative integers .
- Step 3: Apply the stars-and-bars formula: .
Answer
.
Why not the others: computes ; is an arithmetic rounding error; computes ; calculates without accounting for the leading digit constraint .
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