Multiples and factors

When “a” divided by “b” is exact, we say that “a” is a multiple of “b”, or “b” is a factor (or divisor) of “a”, or “a” is divisible by “b”.

Example: 3 is a factor (or divisor) of 15 and 15 is a multiple of 3.

We write: fact (15) or 

We calculate the multiples of a number by multiplying this number by another number. Example:

We find the factors of a number by doing all the divisions with the lower numbers till the quotient is bigger than the divisor. When the division is exact, the quotient is a factor too.

Example: 20 : 5 = 4   Then 4 and 5 are factors of 20.
Fact(20) = {1, 20, 2, 10, 4, 5} and we put them in order    Fact(20) = {1, 2, 4, 5, 10, 20} 

 

Exercises:

1.- Write down 3 multiples of 18.

2.- Find all the divisors of 18, 27 and 40

 

 

Solutions: 1.-  {18, 36, 54, 72, 90, 108,...} 2.- Fact(18)={1,2,3,6,9,18}; Fact(27)={1,3,9,27}; Fact(40)={1,2,4,5,8,10,20,40}