Grade 5 : Questions and Answers on Prime and Composite Numbers
I. Choose the right answer and fill in the blank:
(i) The only even prime number is ….…..
(a) 0
(b) 2
(c) 4
(d) 6
(ii) The number which is neither prime nor even ….…..
(a) 1
(b) 2
(c) 10
(d) 100
(iii) The number which has more than 2 factors is called a ….…..
(a) Even
(b) Odd
(c) Prime
(d) Composite
(iv) ….….. is the smallest composite number.
(a) 0
(b) 2
(c) 3
(d) 4
(v) A prime number has only ….….. factors.
(a) 0
(b) 1
(c) 2
(d) 3
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(vi) A pair of numbers that do not have any common factor other than 1 are ….….. numbers.
(a) Even
(b) Co-prime
(c) Twin prime
(d) Prime
(vii) The smallest odd prime number is:
(a) 1
(b) 3
(c) 5
(d) 7
(viii) Which of the following is a prime number?
(a) 9
(b) 11
(c) 21
(d) 15
(ix) Which of the following even number is prime?
(a) 2
(b) 4
(c) 16
(d) 26
(x) Which of the following is a composite number?
(a) 19
(b) 21
(c) 23
(d) 29
(xi) Number formed by multiplying the first three prime numbers is:
(a) 50
(b) 40
(c) 30
(d) 20
Answers:
(i) (b) 2
(ii) (a) 1
(iii) (d) Composite
(iv) (b) 2
(v) (c) 2
(vi) (b) Co-prime
(vii) (b) 3
(viii) (b) 11
(ix) (a) 2
(x) (b) 21
(xi) (c) 30
II. Write true or false:
(i) 1 is a prime number.
(ii) There are 8 prime numbers between 1 – 20.
(iii) 12 is a prime number.
(iv) 21 has 4 factors – 1, 3, 7 and 21.
(v) 4, 6, 7, 8 and 9 are composite numbers.
(vi) Consecutive numbers are always co-prime.
Answers:
(i) false
(ii) true
(iii) false
(iv) true
(v) false
(vi) true
III. Choose all prime numbers:
12 19 7 8 9 11 15
13 24 27 23 34 37 36
Answers:
19, 7, 11, 13, 23, 37
IV. Write all the composite numbers less than 30.
Answers:
4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21,22, 24, 25, 26, 27, 28
V. Write all the prime numbers less than 20.
Answer: 2, 3, 5, 7, 11, 13, 17, 19
VI. Check if the given pair of numbers are co-primes:
(i) 15 and 38
(ii) 25 and 26
(iii) 12 and 18
Answers:
(i) co-primes
(ii) co-primes
(iii) not co-primes
VII. Fill in the blanks:
(i) The numbers with just 2 factors are called ……………………… numbers.
(ii) Smallest even prime number is ……………………….
(iii) Numbers with more than 2 factors are called ……………………… numbers.
(iv) 1 is neither ……………………… nor ……………………….
(v) All composite numbers have more than ……………………… factors.
Answers:
(i) prime
(ii) 2
(iii) composite
(iv) prime, composite
(v) 2
VIII. Circle all the composite numbers in the given box:
Answers:
15, 9, 21, 49, 35, 3393, 51
IX. Write all the prime numbers between:
(i) 1 and 20
(ii) 20 and 40
(iii) 40 and 60
(iv) 60 and 80
(v) 80 and 100
Answer:
IX. (i) 2, 3, 5, 7, 11, 13, 17 and 19.
(ii) 23, 29, 31, 37.
(iii) 41, 43, 47, 53, and 59.
(iv) 61, 67, 71, 73, and 79.
(v) 83, 89 and 97.
X. Write all the composite numbers between 1 and 40.
Answer:
X. 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40.
XI. Fill in the blanks:
(i) The smallest prime number is …………….
(ii) The largest two-digits prime is …………….
(iii) Every prime number except ……………. is odd
(iv) ……………. is neither a prime nor a composite number.
(vi) Since 4 has 3 factors, 4 is a ……………. number.
Answer:
XI. (i) 2
(ii) 97
(iii) 2
(iv) 1
(vi) composite
XII. State whether the following statements are true or false.
(i) There is only one natural number that is neither a prime nor a composite.
(ii) The odd number are prime numbers.
(iii) All even numbers are composite numbers.
(iv) The sum of two prime numbers is always an even number.
(v) 33 is a prime number.
Answer:
XII. (i) True
(ii) False
(iii) False
(iv) False
(v) False
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