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

**CBSE CLASS 6 MATHEMATICS**

**Playing With Numbers – Chapter 3**

**Short Answer Type Questions**

**Answer the following (2 marks):**

**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?**

** ANSWERS**:

**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.**