OlympiadMediumCombinatorics10–12
How many four-digit numbers have digits that strictly increase from left to right?
Quantos números de quatro algarismos têm algarismos estritamente crescentes da esquerda para a direita?
Answer options
Solution
Step 1 of 3
- 1.A strictly increasing string of digits cannot contain , since would have to come first and a number cannot start with .