# Number system class 9 mcq

### number system class 9 mcq

Which of the following is not a natural number?
a) 0
b) 1
c) 2
d) 3

Which of the following is a prime number?
a) 10
b) 15
c) 17
d) 20

Which is the smallest composite number?
a) 1
b) 2
c) 3
d) 4
Explanation: A composite number is a positive integer greater than 1 that is not prime and has divisors other than 1 and itself. The smallest composite number is 4.

Which of the following is an irrational number?
a) 0.5
b) √2
c) 2/3
d) 1.5
Explanation: An irrational number is a number that cannot be expressed as a fraction or a terminating or repeating decimal. √2 is an example of an irrational number

Which is the largest perfect square less than 100?
a) 81
b) 88
c) 95
d) 100
Explanation: A perfect square is a number that is the square of an integer 81 is the largest perfect square less than 100.

Which of the following is a rational number?
a) √5
b) -3.14
c) 0.75
d) π (pi)
Explanation: A rational number is a number that can be expressed as a fraction or a terminating or repeating decimal. 0.75 is a rational number.

Which of the following is a co-prime pair?
a) (8, 12)
b) (10, 15)
c) (9, 18)
d) (14, 21)
Explanation: Co-prime numbers are numbers ,that have no common factors other than 1. 10 and 15 are co-prime because their only common factor is 1.

Which of the following is a rational number but not an integer?
a) -3
b) 0
c) 0.5
d) √2
Explanation: A rational number can be expressed as a fraction or a terminating or repeating decimal. 0.5 is a rational number but not an integer.

Which is the largest prime number less than 20?
a) 15
b) 17
c) 19
d) 20

Which of the following is a composite number?
a) 1
b) 2
c) 3
d) 4
Explanation: A composite number is a positive integer greater than 1 that is not prime and has divisors other than 1 and itself. 4 is a composite number.

The decimal representation of which of the following rational numbers will be non-terminating and non-repeating?
a) 1/2
b) 2/5
c) 1/3
d) 3/4
Explanation: The decimal representation of 1/3 is 0.3333…, which, is non-terminating and non-repeating.

The number 0 is a:
a) Whole number
b) Rational number
c) Irrational number
d) None of the above
Answer: d) None of the above
Explanation: 0 is not considered a whole number, rational number, or irrational number. It is a unique number on its own.

Which of the following numbers is both rational and an integer?
a) 3/4
b) 0.5
c) -5
d) √2

Which of the following is not a real number
a) √9
b) -1.5
c) 0
d) i
Explanation: i represents the imaginary unit and is not a real number. Real numbers include integers, fractions, decimals, and irrational numbers.

The sum of two rational numbers is always:
a) An integer
b) A rational number
c) An irrational number
d) None of the above

The product of two irrational numbers can be:
a) An integer
b) A rational number
c) An irrational number
d) None of the above

Which of the following is not a prime factor of 24?
a) 2
b) 3
c) 4
d) 6
Explanation: The prime factors of 24 are 2 and 3. 4 is not a prime factor because it can be further divided by 2.

What is the smallest positive integer, that is a multiple of both 5 and 7
a) 10
b) 14
c) 21
d) 35
Explanation: The smallest positive integer that is a multiple of both 5 and 7 is their least common multiple, which is 35.

The number 0.333… is an example of a/an:
a) Irrational number
b) Whole number
c) Terminating decimal
d) Repeating decimal
Explanation: The number 0.333… represents a repeating decimal in which the digit 3 repeats infinitely.

Which of the following numbers is a perfect cube?
a) 8
b) 16
c) 27
d) 36
Explanation: A perfect cube is a number that can be expressed as the cube of an integer. 27 is the cube of 3.

Which of the following is a prime factor of 40?
a) 2
b) 4
c) 5
d) 8
Explanation: The prime factors of 40 are 2 and 5. 2 is a prime factor because it is a prime number and divides 40 without leaving a remainder.

The square root of which number is an irrational number?
a) 9
b) 16
c) 25
d) 36

Which of the following is a prime number?
a) 21
b) 27
c) 29
d) 33

What is the value of 0.5 as a fraction in the simplest form?
a) 1/2
b) 2/4
c) 5/10
d) 10/20