# Playing With Numbers – Chapter 3/Short Answer Type Questions.

CBSE CLASS 6 MATHEMATICS
Playing With Numbers – Chapter 3

1. Write the multiples of 8 and 9. Find their first two common multiples. Find the Lowest Common Multiple (LCM)?
2. Classify the following numbers as prime and composite numbers:
41, 42, 43, 44, 45, 46, 47, 48
3. Write all the factors of 50
4. What are twin primes? Give three pairs of twin primes.
5. What are co-prime numbers? Give two examples.
6. Write the prime factorisation of 36.
7. Using the divisibility rules, check if 726352 is divisible by 4 and 8.
8. Express the following as the sum of two odd primes.
i) 48
ii) 64
9. Express the following as the sum of three odd primes.
i) 18
ii) 38
10. Find the LCM of the following numbers:
i) 3 and 7
ii) 6 and 5
Observe a common property in the obtained LCMs. Is LCM the product of two numbers in each case?

1. Multiples of 8 are 8, 16, 24, 32, 40, 48, 56, 64, 72, 80……..
Multiples of 9 are 9, 18, 27, 36, 45, 54, 63, 72, 81, 90……….
Common Multiples are 72……
LCM = 72

2. Prime Numbers are 41, 43, and 47.
Composite Numbers are 42, 44, 45, 46, and 48.

3. Factor pairs of 50 are 1 x 50, 2 x 25, and 5 x 10.
Factors of 50 are 1, 2, 5, 10, 25, and 50.

4. Two prime numbers whose difference is 2 are called twin primes.
Three pairs of twin primes are 5 – 3 = 2, 7 – 5 = 2, 13 – 11 = 2.

5. Two numbers having only 1 as a common factor are called co-prime numbers.
4 and 15 are co-primes.
6 and 7 are co-primes.

6. Prime factors of 36 are 2 x 2 x 3x 3.

7. 726352
A number with 3 or more digits is divisible by 4 if the number formed by its last 2 digits is divisible by 4.
Here last two digits are 52, which is divisible by 4.
So 726352 is divisible by 4.
A number with 4 or more digits is divisible by 8, if the number formed by the last 3 digits is divisible by 8.
Here last 3 digits are 352, which is divisible by 8.
So 726352 is divisible by 8.

8. i) 48 = 41 + 7
ii) 64 = 61 + 3

9. i) 18 = 2 + 3 + 13
ii) 38 = 2 + 5 + 31

10.i) Multiples of 3 are 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42……
Multiples of 7 are 7, 14, 21, 28, 35, 42, 49, 56, 63, 70……..
Common Multiples are 21, 42……
LCM = 21.
ii) Multiples of 6 are 6, 12, 18, 24, 30, 36, 42, 48, 54, 60………
Multiples of 5 are 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60……
Common Multiples are 60…..
LCM = 60.
Here 3 and 7 are co-primes. Also 6 and 5 are co-primes.
In each case LCM is the product of two numbers.