# Mathematics Class 6 NCERT Solutions: Chapter 3 Playing With Numbers Exercise 3.5-Part 1

Q.1 Which of the following statements are true:

(a) If a number is divisible by 3, it must be divisible by .

Ex. 6 is divisible by 3, but not by 9.

(b) If a number is divisible by 9, it must be divisible by .

So, if a number is divisible by 9, it must be divisible by .

(c) If a number is divisible by 18, it must be divisible by both .

Ex. 30 is divisible by 3 and 6 both, but it is not divisible by 18.

(d) If a number is divisible by 9 and 10 both, then it must be divisible by .

So, If a number is divisible by 9 and 10 both, then it will also be divisible by 90.

(e) If two numbers are co-primes, at least one of them must be prime.

Ex. 15 and 32 are co-prime and also composite.

(f) All numbers which are divisible by 4 must also by divisible by 8.

Ex. 20 is divisible by 4 but not by 8.

(g) All numbers which are divisible by 8 must also by divisible by 4.

Ex.

So, if a number is divisible by 8, then it will also be divisible by 2 and 4.

(h) If a number is exactly divides two numbers separately, it must exactly divide their sum.

Ex. 2 divide 4 and 8 as well as 12.

(i) If a number is exactly divides the sum of two numbers, it must exactly divide the two numbers separately.

Ex. 2 divides 14, but does not divide 9 and 5.

Q.2 Here are two different factor trees for 60. Write the missing numbers.

(a)

As and

(b)

As ,

Q.3 Which factors are not included in the prime factorization of a composite number?