1. Current Average Age :

   • The average age of the family of five members is 20 years.
   • This means the total age of the family is 20×5=10020 \times 5 = 10020×5=100 years.

2. Age of the Youngest Member :

   • The age of the youngest member is 10 years.

3. Total Age of the Other Four Members :

   • Since the youngest member is 10 years old, the total age of the other four members is 100−10=90100 - 10 = 90100−10=90 years.

4. Average Age Calculation a Day Before the Youngest Member's Birth :

   • A day before the youngest member was born, the family had only four members.

   • The total age of these four members would be 909090 years, but each of them would be one day younger. Since one day is negligible in terms of years, we can still consider their combined age as 90 years for practical purposes.

   • Hence, the average age of the four members just before the birth of the youngest member would be:

     Average age = Total age of the four members/Number of members = 90/4 = 22.5 years

So, the average age of the family just a day before the birth of the youngest member was 22.5 years .