Prime Number – Exam Shortcut
Question
Which of the following is not a prime number?
(A) 17 (B) 27 (C) 37 (D) 47
Explanation
17 → factors: 1, 17 → Prime
27 → factors: 1, 3, 9, 27 → Not Prime
37 → factors: 1, 37 → Prime
47 → factors: 1, 47 → Prime
✅ Correct Answer: (B) 27
Shortcut (Exam Tip):
Add the digits of the number.
If the sum is divisible by 3, the number is not prime (except 3).
27 → 2 + 7 = 9 → divisible by 3 → Not Prime
Add the digits of the number.
If the sum is divisible by 3, the number is not prime (except 3).
27 → 2 + 7 = 9 → divisible by 3 → Not Prime
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