1. Knowledge objective: Explore and master the calculation method of subtracting two digits from two digits, and further understand the diversity of calculation methods.

2. Ability goal: cultivate the initial estimation consciousness and the ability to solve practical problems.

1. Emotional goal: to cultivate students' knowledge transfer ability and sense of group cooperation.

Teaching emphasis: master the calculation method of subtracting two digits from two digits.

Teaching difficulties: explore and master the calculation method of two-digit abdication.

(1) Create scenarios and introduce new lessons.

Show the theme map (Xiaodong, Xiaohong and Liang Xiao are skipping rope) with an explanation: Xiaodong, Xiaohong and Liang Xiao are skipping rope during class today, and the teacher made a statistical table of the competition results. Please have a look and tell us what mathematical information you got from the statistics.

The students looked at their watches and reported that Xiaodong jumped 62 times, Xiaohong jumped 48 times and Liang Xiao jumped 70 times.

(2) Explore new knowledge and algorithms from the problem scenario.

1, according to the mathematical situation and information, put forward related questions.

In the group, talk about what math problems you can ask from the statistics.

Student report: How many times does Xiaodong jump than Xiaohong? How many times does Liang Xiao jump more than Xiao Hong?

How many times does Xiaohong jump less than Xiaodong? How many times does Xiaohong dance less than Liang Xiao?

Or did Xiaodong and Xiaohong jump a few times? How many times did Liang Xiao and Xiao Hong dance? How many times did Xiaodong and Liang Xiao dance?

Students solve these problems according to them.

Let the students say what they think. How to form?

62 – 48 = 70 – 48 = 70 – 62 =

62 + 48 = 48 + 70 = 62 + 70 =

2. Explore the algorithm.

First, let the students estimate the following 62–48 =, which may be equal to several, and then let the students verify it through specific calculations.

You can communicate in groups and help each other if you have difficulties.

Report to the group (allow students to use various algorithms)

(1), I think 62-40 = 22, 22-8 = 14, and I will calculate the two-digit number and subtract the integer ten, so I will take 48 as 40 first, and then subtract 8 after subtracting 40, so I will subtract 8 and so on 14.

(2), I think 62-50 = 12, 12 = 14, 48 is regarded as 50, and after 50 is subtracted, we add 2, and so on.

(3) I don't think 2 can be subtracted from 8, so I borrowed 10 from 10, which becomes 12-8 = 4, and the number borrowed from 10 becomes 60-10-40 =/.

Adopt the method of "ten people borrow one is not enough".

(4), with vertical calculation. .

There are various methods, as long as the method is correct.

3. Compare the simplicity of several algorithms.

Please talk about the above algorithm, which is simpler and less prone to mistakes.

Teachers can also express their views, such as: teachers think that the calculation method of "ten loans are not enough" is simpler and less prone to mistakes.

Students can choose the method they accept according to their own situation.

(3) Practical application.

1, completed 70–48 = 70–62 =

When giving collective feedback, talk about your own algorithm.

2. "Think about it" on page 62 of the textbook.

When students finish independently and give feedback collectively, talk about their own algorithms.

3. Title 1 on page 63 of the textbook.

When the students finish independently and give collective feedback, the groups check each other and talk about the problems they found during the inspection. For example, one is not borrowed, and the digits are not aligned.

Question 2 on page 63 of the textbook.

Let the students understand the picture first. In their own words: Naughty bought a badminton racket with 50 yuan, and the salesgirl found him with 29 yuan. How much does it cost to buy a badminton racket?

Finally, organize students to communicate and let them talk about their ideas.

5. Question 3 on page 63 of the textbook.

Make clear the meaning of the question. Students should finish it independently, and the answer to "() +40" is not. Students can guess that "()" may be 0 or 4. If "()" is other numbers, then there is no home.

(4) summary.