Which number is prime?
- A.21
- B.27
- C.29 ✓
- D.33
Explanation: 21=3×7, 27=3×3×3, 33=3×11 — all have factors besides 1 and themselves. 29 has none.
Class 6 IMO Mathematics Olympiad practice · Number Sense · Factors, Multiples & Primes
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