Let me give you an example (I think it is very difficult, although I am good at math and in Grade 5): There are several natural numbers greater than 0, and their average value is 10. If the largest one is removed, the average value of the remaining numbers is 9; If the smallest one is removed, the average of the remaining numbers is 1 1. What are these numbers at most? What is the biggest one?

Answer:

Solution: Set the number of (A+ 1).

10×(a+ 1)-9a

= 10a+ 10-9a

=a+ 10

10(a+ 1)— 1 1a

= 10a+ 10- 1 1a

= 10-a a+ 1= 10

9+ 10= 19

10-a & gt； 0

A max = 9

A: The maximum number is 10 and the maximum number is 19.