Ncert Solutions For Class 6 Maths Ex 3.1

Ncert Solutions For Class 6 Maths Chapter 3 Ex 3.1

1. Find the sum of any two numbers ?

(a) odd numbers

(b) even numbers

SOLUTION (a) SOLUTION (b)

e.g. 6 + 3 = 9 e.g. 12 + 14 = 26

 

2. Write down the prime numbers less than 20.

SOLUTION:

The numbers which are divisible by itself is known as prime numbers . prime numbers which are less than 20 are,

2 , 3 , 5 , 7 , 11 , 13 , 17 , 19.

 

3. Write down the composite numbers less than 20.

SOLUTION:

The numbers which are not prime numbers is known as composite numbers. The composite numbers which are less than 20 are,

4 , 6 , 8 , 9 , 10 , 12 , 14 , 15 , 16 , 18 .

 

4. The numbers 31 and 13 are prime numbers. Both these numbers have same digits 1 and 7. Find such pairs of prime numbers up to 100.

SOLUTION:

(79 , 97) (37 , 73) (17 , 71)

 

5. Express the following in the form of sum of two odd primes.

SOLUTION :

(a) 24 = 5 + 19

(b) 44 = 7 + 37

(c) 18 = 7 + 11

(d) 36 = 31 + 5

 

6. Find any three pair of prime numbers whose difference is two.

SOLUTION:

Two prime numbers whose difference is ‘2’ is also called as twin primes or twin prime number.

3 pairs : (41 , 43) ( 73 , 71) (5 , 3)

 

7. Express the following numbers in the form of sum of three odd primes.

SOLUTION:

(a) 53 = 31 + 3 + 19

(b) 61 = 19 + 11 + 31

(c) 31 = 19 + 5 + 7

 

8. Write down the 3 pairs of prime numbers which is less than 20 and also whose sum is divisible by 5.

SOLUTION:

(*) 17 + 3 = 20 (5 x 4 = 20. It is divisible by 5)

(*) 13 + 2 = 15 (5 x 3 = 15. It is divisible by 5)

(*) 11 + 19 = 30 ( 5 x 6 = 30. It is divisible by 5)

 

9. FILL IN THE BLANKS.

(*) 1 is neither _____ nor ________. ans: (composite , prime)

(*) The number which has only one factor is called _________. ans: (prime number)

(*) The smallest composite number is ________. ans: ( 4 )

 

10. TRUE OR FALSE.

(*) The sum of two prime numbers is always even. Ans : false

e.g. 3 + 2 = 5 (i.e) odd

(*) The product of three odd numbers is odd. Ans : true

e.g. 5 x 7 x 3 = 105 (i.e) odd

(*) The product of two even numbers is always even. Ans : true

e.g 2 x 4 = 8 (i.e) even

6 x 2 = 12 (i.e) even

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