Subtraction exercises of abdication within 20 years in first grade mathematics

Objective: To put forward practical problems solved by subtraction with the help of situation diagram, and to cultivate students' observation ability and ability to find and solve problems.

Answer: 1 1-5 = 6 (only). A: There are six chickens left.

Analysis: first collect complete information according to the chart, and then calculate it in the form of table.

2. Xiaoqing wants to practice calligraphy 16 China calligraphy, with 8 words left. How many words did he write?

Objective: To investigate the practical problems solved by subtraction, so that students can further understand the significance of subtraction and improve their ability to solve practical problems.

Answer: 16—8=8 (pieces). He wrote eight words.

Analysis: Drawing can help to analyze the quantitative relationship and reflect the structural reconstruction calculation of the problem.

There are 15 rabbits, 8 sheep and 6 cows in the zoo.

(1) How many sheep and cows are there?

(2) There are 5 white rabbits and how many black rabbits?

Objective: To cultivate students' ability to observe and collect information and solve problems from different angles.

Answer: (1)8+6= 14 (only). A: There are 14 sheep and cattle.

(2)15-5 =10 (only). A: There are 10 black rabbits.

Analysis: the problem (1) finds the total and adds it. Problem (2) Find the other part of the known sum and use subtraction. Let students realize that different questions are raised and the specific methods to solve them are different.

4. Xiao Li planted 14 plants and Xiaowen planted 7 plants. How many more trees does Xiaoli plant than Xiaowen? How many trees have Xiaowen planted less than Xiaoli?

Objective: To study the consolidation exercise after Example 6.

Answer: 14—7=7 (tree). A: Xiaoli planted 7 more trees than Xiaowen, and Xiaowen planted 7 fewer trees than Xiaoli.

Analysis: Guide students to communicate the relationship between the problem of "what is the ratio" and the original subtraction model by drawing, and get the thinking method to solve the problem. The latter problem can be reduced by transforming ideas, and both problems can be solved by 14-7 = 7.