2.1250+230-1280 = 200 people.

3, (280+30)÷2= 155

This needs to be explained. Think of it this way: mom eats four apples a day, and she hasn't finished them by the planned number of days. What should I do? Mom wants to eat two more and make six every day to see if she can finish eating. As a result, I ate the first extra 18 and had to buy eight. That is to say, the second way is more than the first way (18+8)=26, because the second time is to eat two more apples a day, so it can be concluded that the planned days must be 26÷2= 13 (days), so there is13× 4+66. This is a typical profit and loss problem: (1) once there is a surplus (surplus) and once there is a deficit (deficit). The formula can be used: (surplus+deficit) ÷ (the difference between two distributions per person) = number of people.

(2) There are two surpluses (surpluses), and the formula can be used as follows: (large surplus-small surplus) ÷ (the difference between two distributions per person) = number of people.

(3) If twice is not enough (loss), the formula can be used: (big loss-small loss) ÷ (the difference between two distributions per person) = number of people.

(4) One time was not enough (deficit), and the other time was just finished. The formula can be used: deficit ÷ (the difference between two distributions per person) = number of people.

(5) One time there is surplus, and the other time it is just used up. The formula can be used: surplus ÷ (the difference between two distributions per person) = number of people.