ADDITIONAL QUESTIONS AND ANSWERS
1). Write the first four multiples of the following:
a) 12
Ans. 12 x 1 = 12, 12 x 2 = 24, 12 x 3 = 36, 12 x 4 = 48
∴The first four multiples of 12 are 12, 24, 36, 48
b) 18
Ans. 18 x 1 = 18, 18 x 2 = 36, 18 x 3 = 54, 18 x 4 = 72
∴the first four multiple of 18 are 18, 36, 54, 72
c) 24
Ans. 24 x 1 = 24, 24 x 2 = 48, 24 x 3 = 72, 24 x 4 = 96
The first four multiples of 24 are 24, 48, 72, 96
2). Find the LCM of :
a) 12,30
Ans. LCM = 2 x 2 x 3 x 5
=60.
b) 20, 25, 30
Ans. LCM = 2 x 2 x 3 x 5 x 5
= 300
c) 16, 24, 26
Ans. LCM = 2 x 2 x 2 x 2 x 3 x 3 = 144
3). Find the factors of
a) 30 b )36 c) 45
Ans.
a) 30 = 2 x 3 x 5
b) 36 = 2 x 2 x 3 x 3
c) 45 = 3 x 3 x 5
4). Find the multiple of 7 upto 100.
Ans. 7 x 1 = 7, 7 x 2 = 14, 7 x 3 = 21, 7 x 4 = 28, 7 x 5 = 35, 7 x 6 = 42, 7 x 7 = 49, 7 x 8 = 56, 7 x 9 = 63, 7 x 10 = 7, 7 x 11 = 77, 7 x 12 = 84, 7 x 13 = 91, 7 x 14 = 98.
∴the multiple of 7 upto 100 are 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91 and 98.
5). Write all the prime numbers between 20 – 60.
Ans. 23, 29, 31, 41, 43, 47, 53, 59 are the prime numbers between 20 – 60.
6). Write all the composite number between 10 – 40
Ans. 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39 are the composite numbers between 10 – 40.
7). Using divisibility tests determine which of the following numbers are divisible by
a)625 b)1212
Ans. a) 625
Sum of all digits = 6 + 2 + 5 = 13, which is not divisible by 3 625 is not divisible by 3.
Ans. b) 1212
Sum of all digits = 1 + 2 + 1 + 2 = 6, since 6 is divisible by 3 1212 is divisible by 3.
8). Write the missing factors in each of the following:-
Ans.
9). If the LCM and HCM of any two numbers are 15 and 4 respectively, find the product of the numbers.
Ans. The product of the number = LCM x HCF
= 15 x 4
= 60
∴The product of the numbers = 60
10). Find HCF of
a)12, 16 and 18
Ans. 12 = 2 x 2 x 3
16 = 2 x 2 x 2 x 2 25
28 = 2 x 2 x 7 30
∴HCF = 2 x 2 = 4
b)15, 25 and 30
Ans. 15 = 3 x 5
= 5 x 5
= 2 x 3 x 5
∴HCF = 5
11). State whether true or false
a) If a number is divisible by 2 and 3, it is divisible by 6.
b) The sum of any two odd numbers is even.
c) Two numbers with 1 as a common factor are called prime number.
d) The smallest prime number is an odd number.
e) There are 25 non-composite numbers below 100.
f ) 225 is a multiple of 2.
g) There are no common factors of 39 and 169
Ans.
a) True
b) True
c) True
d) False. the smallest prime number 2 is an even number.
e) True
f) False. 225 is not a multiple of 2
g) False. 13 is a common factor of 29 and 169.