The average age of four brothers is 12 years. If the age of their mother is also included, the average is increased by 5 years. The age of the mother (in years) is?

To solve this problem, we need to follow these steps:

1. First, we need to find the total age of the four brothers. Since the average age is 12 years, and there are 4 brothers, we multiply 12 by 4 to get 48 years.

2. Next, we need to find the total age of the four brothers and their mother. Since the average age increases by 5 years when the mother's age is included, and there are now 5 people, we multiply 5 (the new average age) by 5 (the number of people) to get 25 years.

3. However, this gives us the increase in total age, not the total age itself. So we need to add this to the total age of the brothers. 48 (the total age of the brothers) plus 25 (the increase in total age) gives us 73 years.

4. Finally, to find the mother's age, we subtract the total age of the brothers from the total age of the brothers and the mother. So, 73 (the total age of the brothers and the mother) minus 48 (the total age of the brothers) gives us 25 years.

So, the mother is 25 years old.