Mathematics of Grade Four, Volume II, Decimal Approximation, teaching material analysis:
Students have learned to approximate integers before, and have formed basic learning experience.
Analysis of learning situation:
Arouse students' experience and recall the rounding method before learning.
Teaching objectives:
1, so that students can use the method of "rounding" to reserve a certain number of decimal places and find out the approximate number of decimal places.
2. Cultivate students' analogy ability, and enhance students' understanding of mathematics and confidence in applying mathematics.
Teaching emphases and difficulties:
Key points:
Can correctly find the approximate value of a decimal.
Difficulties:
How to find the approximate value of a decimal accurately
(1) Create situations and review a large number of approximate figures.
(B), determine the objectives, the introduction of new courses
(3) Interactive communication
(4) class summary
Teacher: The height of Doudou is 0.984 meters. 0.984 is an accurate value, so how many meters can we say peas are?
Teacher: If you keep two decimal places, you should omit the third place. The third decimal of 0.984 is "3", which is less than 5, so it is 0.984≈0.98.
Teacher: Where is the approximate value of two decimal places accurate?
Teacher: Can you find the approximate figure of this decimal in other different situations?
Teacher: If you keep the integer, you should omit the decimal part. The first decimal place, that is, the tenth decimal place, is 9, greater than 5, one place ahead, so 0.984≈ 1.
Teacher: Where is the approximate value of the reserved integer accurate?
Teacher: Although the two numbers are equal in size, the accuracy of expression is different. When approximating, the zero after the decimal point cannot be removed.
Teacher: When calculating the approximate value, keep the integer, which means it is accurate to one place. Keep one decimal place, which means accurate to ten places. Keep two decimal places, indicating accuracy to one hundredth. ...
Health: accurate to the second decimal place, that is, percentile.
Student: accurate to one student: ① take an approximate value according to the requirements of the topic. If you keep the integer, it depends on the decimal number. To keep a decimal place depends on the percentile. ..... and then press the "rounding method" to decide whether to give up or enter. (2) In approximation, among the reserved decimal places, the last digit or digit is 0. 0 should be kept, not lost. In order to realize the positive transfer of students' existing knowledge, it is necessary to review the rounding method with examples in life and get a larger approximation, and at the same time educate students in their thoughts and feelings.
Fill in the blanks:
(1) Find the divisor of a decimal, and the number of decimal places should be reserved by the method of (). When the integer is reserved, it means accurate to () bit; When one decimal place is reserved, it shall be accurate to () place; When two decimal places are reserved, it is accurate to () place. .....
(2) The result of the divisor is generally said that 6.0 is more accurate than 6, because 6.0 is accurate to () and 6 is accurate to (), so the "0" at the end of 6.0 cannot be removed.
2. Write the approximate decimal places in the table as required. Keep an integer, a decimal place and two decimal places.
4.808
20.256
1.995
Blackboard design:
Approximate decimal places:
0.984≈0.98
0.984≈ 1.0
Think about it: 0.984≈ 1
When representing approximate value, 0 after decimal point cannot be deleted.