3a- 15； a= 15

The average value of several nonzero natural numbers is 10. If the largest number is removed, the average value of the remaining numbers is 9; If the smallest number is removed, the average value of the remaining number is 1 1. What is the sum of the largest number and the smallest number among these numbers?

Let a ***n number.

Then the sum of all numbers is 10n.

So the maximum number = 10N-9 (n- 1) = n+9.

Similarly, the smallest number =-n+ 1 1.

Obviously the total is 20.

The total number of 79 trees is 25/8 =200.

Other trees are 200-25 = 175.

Therefore, apple trees should be replanted to 175, and should be replanted.

175-25 = 150 trees

Question 89 6

90 exists 346 347 409 4 10 and so on.

95 7 1777-7 1 1 1 1=666