Size comparison of decimals
Orientation of teaching objectives:
1. In the specific problem situation, I experienced the process of exploring the fractional size comparison method, experienced the diversification of problem-solving strategies, and mastered the general method of solving practical problems around me by the size comparison method.
2. Cultivate students' thinking ability of guessing, verifying, comparing and summarizing in independent and cooperative activities.
3. Further understand the relationship between mathematics and life, infiltrate the idea of concrete analysis of specific problems, and improve students' interest in learning mathematics through diversified inquiry materials.
Teaching focus:
Explore and summarize the general methods of decimal size comparison.
Teaching difficulties:
Effectively coordinate the relationship with integer size comparison.
Teaching process:
First, review and review
1 and 3.72 are composed of () ones, () deciles and () percentiles.
2.0.48 is () 0.0 1, and 0.62 is () 0.0 1.
3. In decimals, the decimal point is the boundary, followed by the () part.
4. The first digit to the right of the decimal point is (), the second digit is (), and the third digit is ().
Second, introduce new knowledge.
Stick a small rectangular card on the blackboard.
1, students, today the teacher brought some cards, not ordinary cards. There is a number hidden behind each card. Question: If these two sets of cards represent two integers, which integer do you think will be bigger? Why?
2. immediately put a decimal point between the two boxes and ask: which decimal point do you think will be bigger now?
3. Students guess the size. (Default: large in front; Big back; Not sure)
4. uncover the topic. This involves what we are going to discuss today: "the size comparison of decimals" and the topic of blackboard writing.
Third, explore
(1) Preliminary research and construction.
1, show me your long jump report card.
The teacher here has the long jump report card brought by our school sports meeting. Unfortunately, it is a bit incomplete, but according to the information in it, can you confirm anything?
Event: Men's Long Jump
Name: Xiaohong Xiaoming Xiao Qiang
Achievement: 2.84m 3.05m 2. □ 8m。
Nanometer ii
2. Student feedback: Xiao Ming jumped farthest (first place).
3. How do you compare? Summary: Find the first place from the integer part of the comparison decimal.
4. Who was the second place? What would it be like if Xiao Qiang won the second place? (Default: 8 or 9 □ will be filled in)
5. 9 in the box is 2.98 meters. Can you verify that 2.98 is greater than 2.84 with the knowledge you have learned before? (After thinking independently for a moment)
Teacher: Now let's exchange your ideas in the group and see which group has the most ideas.
Preset: (derived from generations: composed of several decimal units)
A, compared with the integer part, bit by bit.
B, from the counting unit ratio. 2.98 has 298 0.0 1, 2.84 has 284 0.0 1, and 298 is greater than 284.
C. convert meters into centimeters. 2.98m = 298cm, 2.84m = 284cm. 298 is bigger than 284.
D, using the relationship between fractions and decimals. 2.98=298/ 100,2.84=284/ 100……
6. Xiao Qiang is the second place. You can also compare the size of 2.88 and 2.84 at □. How to compare them quickly?
7. What would you think if Xiao Qiang won the third place? (Fill in 0 to 7 in □)
(2) Review and verification.
1. If you want to know their size, just turn them over. Ask two students to come up as assistants.
(Choose a male classmate and a female classmate purposefully, and choose a set of numbers to represent the male and female classmates respectively. )
2. How do you think to translate these two decimals quickly?
□□。 □□ □□。 □□□
3.▲ After turning over the integer part of 10, Q: Did you compare it? Why? Then what should I do?
▲ The flop design of the tenth place is as follows-(Let's flop first in life. Before turning around, ask: What number do you want for the tenth place? What number do you want him to be? After the flop, ask another life: What number do you want to turn now? ) Is the game over? Why?
▲ The design of the' flop' of the percentile is as follows-(Let another life flop first, and then ask: Do you think victory is in hand now? Why? -Guide students to say several possibilities)
▲ Open 10.58 10.57□ according to the answer.
▲ After the flop, ask: Why are you depressed? Don't you have one left? What if it's 9? Didn't you just like 9? (Generation-based assessment)
▲ What if the number is changed to 10.58 10.58? What about the zero in the box?
▲ If two numbers are 10.58 10.587, how to make the first number bigger without adding a new number? You can change the position of the variable or the decimal point. )
Review: How did we compare the sizes of decimals just now? Share your thoughts with your deskmate?
Comparing the sizes of two decimals, compare the integer part first, and the number with the larger integer part will be larger; Integer partial phase
Similarly, if we compare the tenth digit, the largest digit in the tenth digit will be even larger; ……
(board calligraphy)
5. Comparison: Is there a difference between the size comparison of decimals and the size comparison of integers?
Fourth, application
1. Fill in ">", "
3 yuan ○2.6 yuan 6.35m ○ 6.53m4.723 ○ 4.79 0.458 ○ 0.54.
2. First, use a straight line to represent the following numbers, and then compare the sizes of two numbers in each group.
0.09、0. 12、0.28、0.3、0.4、0.04
(The number on the axis increases as you move to the right. )
judge
( 1) 10.8 > 1.08 ( )
(2) The ratio of 2.31to 2.299 is 2.3 1 < 2.299 because there are many digits in 2.299. ( )
(3) 514.5m > 5.455438+0km ()
(4) 7. 15 < 7 .□ 6, only 2 ~ 9 can be filled in the box. ( )
Fifth, expand and deepen.
How many different decimals can be formed by using number cards 2, 3, 4 and decimal points (without repetition or omission)? Can you sort it in descending order? (think independently first, and then cooperate and communicate in groups if you have difficulties)
Abstract of intransitive verbs
What do you gain or regret from this lesson?