Page 43 - Math 7

Operations on Whole Numbers

EXERCISE 3.2
General Section -Classwork
1. i) 6 is a multiple of 3. So, L.C.M. of 3 and 6 is 6.
ii) 2 and 3 are prime numbers. So, L.C.M. of 2 and 3 = 2 × 3 = 6.
iii) 4 is a composite number and 5 is a prime number. They are not exactly
divisible to each other. So, L.C.M. of 4 and 5 = 4 × 5 = 20.
iv) 4 and 9 are composite numbers and they do not have any common prime
factors So, L.C.M. of 4 and 9 = 4 × 9 = 36.
Let's investigate the ideas from the above facts. Tell and write the L.C.M. of
a) 2 and 6 is ............. b) 4 and 8 is ............. c) 6 and 18 is .............

d) 2 and 5 is ............. e) 5 and 7 is ............. f) 7 and 11 is .............

g) 5 and 6 is ............. h) 3 and 8 is ............. i) 9 and 10 is .............

j) 4 and 9 is ............. k) 9 and 8 is ............. l) 10 and 21 is .............
2. Let's take any two composite numbers 10 and 15. They have a common prime
factor. Take the bigger number 15 and think of its multiples.
15 × 1 = 15 is not the multiple of 10.
15 × 2 = 30 is the multiple of 10.
So, L.C.M. of 10 and 15 is 30.
Let's follow the similar process and tell and find the L.C.M. of
a) 6 and 9 is ....................... b) 8 and 12 is .....................

c) 10 and 15 is ..................... d) 12 and 18 is .....................

e) 8 and 20 is ................... f) 15 and 25 is .....................

Creative Section - A
3. Let's write the sets of the first ten multiples and the sets of common multiples
of these pairs of numbers. Then, find their L.C.M.
a) 2, 3 b) 3, 4 c) 4, 6 d) 6, 9 e) 8, 12

4. Let's find the L.C.M. of the following numbers by factorization method.
a) 6, 9 b) 9, 12 c) 12, 18 d) 14, 21

e) 4, 6, 8 f) 8, 12, 18 g) 10, 15, 25 h) 14, 21, 35

5. Let's fnd the L.C.M. of the following numbers by division method.
a) 8, 12 b) 14, 21 c) 30, 45 d) 12, 15, 20

e) 12, 16, 24 f) 20, 30, 40 g) 45, 60, 90 h) 72, 90, 120

Approved by Curriculum Development Centre, Sanothimi, Bhaktapur 41 Vedanta Excel in Mathematics - Book 7