2.85-29=56 85-56=29

200+ 127=327 327-200= 127

69-27=42 27+42=69

3. 1988、570、75 1、25 1 29 1、233、405、373

4. The title is abbreviated

(1) 1099 checking calculation:1099-429 = 5701099-570 = 429.

(2) Checking calculation125: 857-125 = 732 732+125 = 857.

(3)564 checking calculation:1532-564 = 968 968+564 =1532.

5.79、230、268、 149

6. Short title

(1) There are 2570 pear trees and orange trees in the orchard, including pear trees 1642. How many orange trees are there?

Answer: 2570- 1642 = 928 (tree)

(2) There are 2570 pear trees and orange trees in the orchard, including 928 orange trees. How many pear trees are there?

Answer: 2570-928 = 1642 (tree)

7. Short title

(1) The original formula: 50- 10 = 40, the number of subtractions is greater than 5: 50- 15 = 35, and the number of subtractions is greater than 10: 50-20 = 30. It is found that in subtraction, the minuend is unchanged, and the number of subtraction is more than the difference.

(2) In subtraction, the minuend is a constant, and the less the minuend, the more the difference.