Which is not a prime number?

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  1. 61
  2. 47
  3. 51
  4. 59

Answer (Detailed Solution Below)

Option 3 : 51
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Detailed Solution

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Formula used:

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Calculation:

61: Divisors: 1, 61 (Prime)

47: Divisors: 1, 47 (Prime)

51: Divisors: 1, 3, 17, 51 (Not Prime)

59: Divisors: 1, 59 (Prime)

⇒ 51 is not a prime number.

∴ The correct answer is option 3.

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