Page 55 - Maths Class 05
P. 55
Composite numbers have two or more rectangular arrays.
This means a composite 1
number has more than 2 4
4
two factors. 2
1 × 4 = 4
2 × 2 = 4
4 × 1 = 4 1
Prime Factorisation
Prime factorisation is to write a composite number as a product of its prime factors.
Factor Tree Method
Example : Find the prime factorisation of 120.
Solution : Let us define 120 as a product of its prime factors.
120
Factor Tree Method
« First, we find any two factors of 120.
10 × 12
« Then, if the factor is prime, we circle
it.
2 × 5
« If not prime, we factor use again
2 × 6
and circle the primes.
« Continue until we only have primes.
2 × 3
\ The prime factorisation of 120 is 2 × 2 × 2 × 3 × 5.
Division Method
2 120
2 60 Start dividing by the smallest prime factor until you
2 30 cannot divide any more. Then, continue dividing by
the next higher prime factor. Repeat the process
3 15
until you get 1.
5 5
1
\ The prime factorisation of 120 is 2 × 2 × 2 × 3 × 5.
Mathematics-5 55
