I am an odd number. Take away one letter and I become even. What number am I?

How to think about it

1. Taking a letter away from a number only makes sense if the number is spelled out, so write the odd numbers as words: one, three, five, seven, nine.
2. Look for a word that turns into “even” when one letter is removed.
3. S-E-V-E-N minus the S leaves E-V-E-N.
4. Seven is the odd number that becomes even when you drop a letter.

Why “Seven” is the answer

The word “seven” contains the word “even” with a single extra letter at the front, so removing the S turns an odd number into the word even. The riddle uses “even” in its spelling sense, not its mathematical one, and seven is the only odd number word with that property. Checking the other odd numbers quickly confirms it.

Common wrong answers

• Five. Removing any letter from “five” gives “ive”, “fve”, “fie” or “fiv”, none of which is even.
• Eleven. Eleven is odd and contains “even”, but you would have to remove three letters, not one.