### number system class 9 mcq

Which of the following is not a natural number?

a) 0

b) 1

c) 2

d) 3

Answer: a) 0

Which of the following is a prime number?

a) 10

b) 15

c) 17

d) 20

Answer: c) 17

Which is the smallest composite number?

a) 1

b) 2

c) 3

d) 4

Answer: 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

Answer: b) √2

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

Answer: a) 81

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)

Answer: c) 0.75

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)

Answer: b) (10, 15)

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

Answer: c) 0.5

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

Answer: c) 19

Which of the following is a composite number?

a) 1

b) 2

c) 3

d) 4

Answer: 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

Answer: c) 1/3

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

Answer: c) -5

Which of the following is not a real number

a) √9

b) -1.5

c) 0

d) i

Answer: 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

Answer: b) A rational number

The product of two irrational numbers can be:

a) An integer

b) A rational number

c) An irrational number

d) None of the above

Answer: c) An irrational number

Which of the following is not a prime factor of 24?

a) 2

b) 3

c) 4

d) 6

Answer: c) 4

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

Answer: 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

Answer: 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

Answer: c) 27

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

Answer: a) 2

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

Answer: b) 16

Which of the following is a prime number?

a) 21

b) 27

c) 29

d) 33

Answer : c) 29

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

Answer : a) 1/2

Explanation: 0.5 can be expressed as a fraction by writing it as 1/2. The fraction is already in its simplest form.

Which of the following is a rational number?

a) √11

b) -2.5

c) π (pi)

d) -3

Answer: b) -2.5

Explanation: -2.5 can be expressed as the fraction -5/2, making it a rational number.