Question 1195101
On May 20, 2012, Victor’s tenth grandchild was born, and the average (arithmetic mean) age of his other 9 grandchildren was 10 years.
 What will be the average age, in years, of Victor’s 10 grandchildren on May 20, 2013?
:
Originally the total age of the 9 grandkids was 90, in one year the total of those 9 kids will be 99, add 1 for the new guy, you have 100 total, divide that by 10 grandkids and have the average age of 10 again