1, Xiao Mahu miscalculated 28× (□+2) as 28× □+2, so the difference between the obtained result and the correct answer is 54.

2. There are 20 stone benches along the road around the lake in the park, and the distance between adjacent stone benches is 36 meters. As more and more people come to visit the park, the park management office decided to add some stone benches, so that the distance between adjacent stone benches is 24 meters (the original stone benches can be moved). Do you want to add 10 stone benches?

Specific solution

Total length = 36 * 20 = 720, * * 720/24 = 30, 30-20= 10, so add 10.

3. A seven-digit number, the sum of digits on each digit is 55. After adding 2 to this number, you get a new number. The sum of the digits in each digit of this new number is 3, and the original number is 199999?

4. True or false: Is the right angle a straight line? (error)