Page 54 - Maths Class 05

Ü Leave 5, but circle all its multiples.

Ü Leave 7, but circle all its multiples.

All the numbers that are not encircled are prime numbers and all the numbers that are
encircled are composite numbers.

Thus, total numbers of prime numbers from 1 to 100 is 25 and remaining are
composite numbers.

Example : Separate the prime numbers and composite numbers from the following

numbers.

6 7 8 16 28 37

Solution : All the factors of 6 are 1, 3, 6.

All the factors of 7 are 1, 7.

All the factors of 8 are 1, 2, 4, 8.

All the factors of 16 are 1, 2, 4, 8, 16.

All the factors of 28 are 1, 2, 4, 7, 14, 28.

All the factors of 37 are 1, 37.

Numbers having only 2 factors are 7 and 37.

\ 7 and 37 are prime numbers.

Numbers 6, 8, 16 and 28 have more than two factors.

\ 6, 8, 16 and 28 are composite numbers.

Example : Find the prime factors of 48.

Solution : We know that : 48 = 1 × 48

48 = 2 × 24

48 = 3 × 16

48 = 4 × 12

48 = 6 × 8

All the factors of 48 are 1, 2, 3, 4, 6, 8, 12, 16, 24 and 48.

The prime factors out of these factors are 2 and 3.

Mathematics-5 54