Find the common factors of 15 and 25.

A number that divides a particular number completely without leaving any remainder is known as a factor of that number.

Factors of  are 1, 3, 5, 15.

Factors of  are 1, 5, 25.

The common among them are 1, 5.

Hence, the common factors of 15 and 25 are 1, 5.