Discrete Mathematics Multiple Choice Questions on “Number Theory – Prime Numbers”.
1. The number of factors of prime numbers are ___________
a) 2
b) 3
c) Depends on the prime number
d) None of the mentioned
Answer: a
Clarification: A prime number is only divisible by 1 and itself.
2. What is the number ‘ 1’?
a) Prime number
b) Composite number
c) Neither Prime nor Composite
d) None of the mentioned
Answer: c
Clarification: 1 is neither prime number nor composite.
3. All prime numbers are odd.
a) True
b) False
Answer: b
Clarification: 2 is even as well as prime.
4. 3 is the smallest prime number possible.
a) True
b) False
Answer: b
Clarification: 2 is also a prime number.
5. How many prime numbers are there between 1 to 20?
a) 5
b) 6
c) 7
d) None of the mentioned
Answer: d
Clarification: The prime numbers between 1 to 20 are 2, 3, 5, 7, 11, 13, 17, 19.
6. There are finite number of prime numbers.
a) True
b) False
Answer: b
Clarification: There are infinite numbers of primes.
7. Sum of two different prime number is a ____________
a) Prime number
b) Composite number
c) Either Prime or Composite
d) None of the mentioned
Answer: c
Clarification: Eg:- 2 + 3 = 5 a prime, 3 + 7 = 10 a composite.
8. Difference of two distinct prime numbers is?
a) Odd and prime
b) Even and composite
c) None of the mentioned
d) All of the mentioned
Answer: c
Clarification: 3 – 2 = 1 is neither prime nor composite.
9. If a, b, c, d are distinct prime numbers with an as smallest prime then a * b * c * d is a ___________
a) Odd number
b) Even number
c) Prime number
d) None of the mentioned
Answer: b
Clarification: Since a is 2, 2 * b * c * d = Even number.
10. If a, b are two distinct prime number than a highest common factor of a, b is ___________
a) 2
b) 0
c) 1
d) ab
Answer: c
Clarification: HCF of two prime numbers is 1.