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Ex) Find the common multiples of 3 and 4.
Sol) Multiples of 3 = 3,6,9,12,15,18,21,24,27,30,33…………
Multiples of 4 = 4,8,12,16,20,24,28,32,36……………..
Common multiples of 3 and 4 are
Ex) Find the common factors of 12 and 18.
Sol) Factors of 12 = 1,2,3,4,6, and 12
Factors of 18 = 1,2,3,6,9, and 18.
Co-Prime Numbers
 Two numbers are said to be co-prime, If they do not
have any common factors other than ‘1’
 (It is not necessary to be either of them to be prime
numbers.
 That is either one or both may be composite numbers)
A number is divisible by both 2 and 3.
By what other numbers will that number be divisible ?
A number is divisible by 15.
By what other numbers will that number be always
divisible ?