Answer: Page 42: 1, 4, 8, 4 (first calculate that the left is equal to 17, and the maximum on the right is 16, so fill in 4).

10 (the right is equal to 28 and the left is 27, so fill in 10.

Three. 1, 8×3÷6=4 (block) 2,9× 8-56 =16 (block) 3,24 ÷ (2× 3) = 4 (branch).

Page 43: Second, the laws of 1 and -9. 2. Add 1, 2, 3, 4. . . Law.

3. Add 2,4,6,8, 10. . . Law. 4. Divide by 2.

Three. 1, 5×2+24=34 (yuan) 2, 12÷6-2