A number between 50 and 60 is prime, and is also one more than a multiple of 4. Which number is it?
- A.51
- B.53 ✓
- C.57
- D.59
Explanation: 53 is prime and 53 = 4×13 + 1. 59 is prime too, but 59−1=58 is not a multiple of 4. 51 and 57 aren't prime at all.
Class 6 IMO Mathematics Olympiad practice · Number Sense · Factors, Multiples & Primes
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