1, addition problem:

(1) This kind of question is not prompted by braces and small question marks, nor by dotted lines and diagonal lines. Usually, write an addition formula. If the title is given to two formulas, write two addition formulas: one from left to right and the other from right to left.

(2) This kind of question is prompted by curly braces and small question marks, which makes it clear what the question is, so it is usually enough to choose the appropriate method to list the formulas according to the content of the question, and just write one. When the question mark is at the tip of the braces, you will usually find out how many * * * the left and right parts add up to.

2, subtraction problem:

(1) This problem has a dotted line, but it is not clear which side to remove, so you usually need to write two subtraction formulas. Both formulas calculate the total first, then subtract the left part to get the right part, and subtract the right part from the total to get the left part.

(2) This kind of problem has a clear explanation, and both dotted lines and diagonal lines indicate the meaning of taking away. Here, both the part occupied by the imaginary circle and the part crossed by the diagonal line indicate that a part has been removed from the total. In this case, only one formula can be written, but it must be emphasized that the total number of objects must be used for subtraction. It's easy for students to write it out by subtracting what they take from what they have left.

3. Add and subtract mixed questions:

When there are both addition and subtraction graphs in a picture, it is a mixture of addition and subtraction. How to find the first number is easy to make mistakes in the formula of addition and subtraction. Generally, the number in the big box is the first number, not the original total.