Find the common factors of : 

(a) 4, 8 and 12         (b) 5, 15 and 25

(a) 4, 8 and 12 
The factors of 4 are 1, 2, and 4.
The factors of 8 are 1, 2, 4, and 8.
The factors of 12 are 1, 2, 3, 4, 6, and 12.
Therefore, common factors are 1, 2, and 4.

(b) 5, 15 and 25
The factors of 5 are 1 and 5.
The factors of 15 are 1, 3, 5, and 15.
The factors of 25 are 1, 5, and 25.
Therefore, common factors are 1 and 5.