The average age of four brothers is 20 years. When the ageof their father is included, the average age increases by 20%. Find the age of thefather.

Sure, let's solve this step by step:

Step 1: Calculate the total age of the four brothers. The average age of the four brothers is 20 years. So, their total age is 4 brothers * 20 years/brother = 80 years.

Step 2: Calculate the new average age when the father's age is included. The average age increases by 20% when the father's age is included. So, the new average age is 20 years + 20% of 20 years = 24 years.

Step 3: Calculate the total age of the four brothers and their father. The new average age is the total age of the five family members (four brothers and their father) divided by 5. So, their total age is 5 family members * 24 years/member = 120 years.

Step 4: Find the father's age. The father's age is the total age of the five family members minus the total age of the four brothers. So, the father's age is 120 years - 80 years = 40 years.

So, the father is 40 years old.