(i) 15 and 25
15 = 1 15
15 = 3 5
i.e., the factors of 15 are 1, 3, 5 and 15.
Again, 25 = 1 25
25 = 5 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 35
35 = 5 7
i.e., the factors of 35 are 1, 5, 7 and 35.
Again, 50 = 1 50
50 = 2 25
50 = 5 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 20
20 = 2 10
20 = 4 5
i.e., the factors of 20 are 1, 2 , 4, 5, 10 and 20.
Again, 28 = 1 28
28 = 2 14
28 = 7 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.