MATHS CONCEPTS PRIME NUMBERS

HOME (NMMS)

MAIN PAGE (MATHS)

Prime Number Twisted MCQ Challenge

1. Which number looks prime but is actually NOT prime?

97 101 121 103

Correct Answer: 121

121 = 11 × 11. Since it has more than two factors, it is not a prime number.

2. Which number is definitely prime?

91 119 89 143

Correct Answer: 89

91=7×13, 119=7×17, 143=11×13. Only 89 has exactly two factors: 1 and 89.

3. A number is not divisible by 2, 3, or 5. What can we conclude?

It is prime It is composite Cannot be determined It is odd prime

Correct Answer: Cannot be determined

49 is not divisible by 2, 3 or 5, yet 49 = 7 × 7. Therefore more testing is needed.

4. Which of the following has exactly three factors?

9 11 13 17

Correct Answer: 9

Factors of 9 are 1, 3, and 9. Thus it has exactly 3 factors.

5. Which one is NOT a prime number?

191 193 221 197

Correct Answer: 221

221 = 13 × 17. Therefore it is a composite number.

6. What is the smallest prime number?

1 2 3 5

Correct Answer: 2

2 is the only even prime number and the smallest prime number.

7. Which statement is true?

Every odd number is prime Every prime number is odd 2 is the only even prime number All composite numbers are even

Correct Answer: 2 is the only even prime number

2 has exactly two factors and is the only even number satisfying the prime definition.

8. Which number is a square of a prime number?

121 143 187 221

Correct Answer: 121

121 = 11². Since 11 is prime, 121 is the square of a prime number.

9. Which of the following numbers has exactly four factors?

15 17 19 23

Correct Answer: 15

Factors of 15 are 1, 3, 5 and 15. Therefore it has exactly 4 factors. 17, 19 and 23 are prime numbers and each has only 2 factors.

10. Which number is formed by multiplying two consecutive prime numbers?

35 77 143 221

Correct Answer: 35

35 = 5 × 7, and 5 and 7 are consecutive prime numbers. 77 = 7 × 11, 143 = 11 × 13, and 221 = 13 × 17 are not products of consecutive prime numbers.