Number Riddles — Factors, Multiples & Primes (Grades 5–6)
Number riddles combine clues — "I'm a prime number between 10 and 20, and my digits add to 4" — and you use everything you know about factors, multiples, and primes to narrow down the one number that fits every clue.
Understanding number riddles — factors, multiples & primes
The strategy: list the numbers that satisfy the first clue, then cross off any that fail the next, until one remains.
Seeing it in action
Worked example
"I'm a prime between 10 and 20, and my digits add to 4." Who am I?
Primes between 10 and 20: 11, 13, 17, 19.
Digit sums: 11→2, 13→4 ✓, 17→8, 19→10. → 13.
Cross off clues until one number remains.
A common mistake, and the fix
Stopping at the first number that fits one clue.
11, 13, 17 and 19 are all primes between 10 and 20, but only 13 has digits that add to 4 (1 + 3). Check every candidate against every clue before answering.
Try a few
"Even number, factor of 12, greater than 5."
both fit; if "less than 10" → 6.
"Multiple of 5, less than 20, digits add to 5."
5; 50 too big.
"Prime, one-digit, odd, more than 5."
Try it in Numeris.
A short lesson, then practice with feedback on every answer.
Put the reasoning on paper.
Try six fraction, angle, perimeter and area questions with explained answers, for grades 4–6.
Free printable · 3 pagesText version (screen-reader friendly): Draw it. Explain it. Math sample
Want a printable set too?
Practise this skill in Numeris, browse more free math pages, or join our optional resource updates.
All free math pages →