Solution to: Thousand Numbers

All written numbers that contain 'hundred' (two d's) are excluded. Therefore, the number we are looking for must be less than 100.

Numbers that contain 'ninety' (two n's) are also excluded. Numbers that contain 'eighty' are possible.

However, the numbers 89 to 85 are excluded because their written forms contain repeated letters:

• eighty-nine: contains two e's, two i's, and two n's;
• eighty-eight: contains two e's, two i's, two g's, two h's, and two t's;
• eighty-seven: contains three e's;
• eighty-six: contains two i's;
• eighty-five: contains two i's.

'Eighty-four' is possible. Conclusion: the number we are looking for is 84.

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