Question

Find the common factors of:

(i) 15 and 25
(ii) 35 and 50
(iii) 20 and 28

Answer 1

(i) 15 and 25
15 = 1 $\times$ 15
15 = 3 $\times$ 5
i.e., the factors of 15 are 1, 3, 5 and 15.

Again, 25 = 1 $\times$ 25
25 = 5 $\times$ 5
i.e., the factors of 25 are 1, 5 and 25.

Therefore, the common factors of the two numbers are 1 and 5.

(ii) 35 and 50
35 = 1 $\times$ 35
35 = 5 $\times$ 7
i.e., the factors of 35 are 1, 5, 7 and 35.

Again, 50 = 1 $\times$ 50
50 = 2 $\times$ 25
50 = 5 $\times$ 10
i.e., the factors of 50 are 1, 2, 5, 10, 25 and 50.

Therefore, the common factors of the two numbers are 1 and 5.

(iii) 20 and 28
20 = 1 $\times$ 20
20 = 2 $\times$ 10
20 = 4 $\times$ 5
i.e., the factors of 20 are 1, 2 , 4, 5, 10 and 20.

Again, 28 = 1 $\times$ 28
28 = 2 $\times$ 14
28 = 7 $\times$ 4
i.e., the factors of 28 are 1, 2, 4, 7, 14 and 28.

Therefore, the common factors of the two numbers are 1, 2 and 4.