The meaning and nature of decimals
Two. ? Teaching emphases and difficulties:
1.？ Understand the meaning of decimals
2.？ Understand the counting unit of decimals, and master the decimal order table.
3.？ Can read and write decimals correctly.
Three. ? Teaching process:
(A) the meaning of decimals
Divide a whole into several parts on average, 100, 1000 ... such 1 part is one tenth, percentage, one thousandth ... can be expressed in decimals. One decimal place indicates a few tenths, two decimal places indicate a few percent, and three decimal places indicate a few thousandths. ...
1, which means:
(1)0. 1 yuan? 1 yuan is 10 angle, 1 angle is one tenth of a yuan, and the decimal is 0. 1 yuan. 1 yuan is 100 minute, 1 minute is 100 yuan, and expressed in decimal is 0.0 1 yuan.
(2)0. 1 m？ 0.0 1 meter? 1 meter is divided into 10 parts on average, and each part is 1 decimeter, which is one tenth of a meter. The length of each copy can be expressed as 0. 1 m in decimal. 1 m is divided into 100 parts on average, each part is 1 cm, that is, one hundredth of a meter, and the length of each part can be expressed as 0.0 1 m in decimal.
(3) How does the square of1represent 0. 1? First of all: 1 stands for a whole, and a square is regarded as a whole 1, which is divided into 10 points on average, indicating one of them.
2. Practice:
6 jiao = (? 0.6? ) yuan? 9 mm =(？ 0.009? )m 1g =(？ 0.00 1) kg
33.333: The first 3 represents three tens, the second 3 represents three 1, and the third tenth is Theory of Three Represents. It can also represent three 0. 1, three percentiles, three 0.0 1, three thousandths and three 0.00 1.
(2) Counting unit and decimal places
1, decimal counting unit
The units of decimals are one tenth, one hundredth and one thousandth. Write 0. 1, 0.0 1, 0.00 1 ... respectively. The progressive rate between adjacent decimal counting units is ten.
2. Decimal digit sequence table
integer part
small
count
main points
fractional part
count
place
……
ten thousand
place
kilobit
The third number on the right
ten
place
individual
place
tenths
percentile
thousands of
Extreme position
One hundred thousand percentile
Milina Ile
……
count
count
single
place
……
ten thousand
a thousand
one hundred
ten
individual
one-tenth
One percent
Maili
Mitty ... Design Manual
One in a hundred thousand
Not one like ... can be found in ten thousand.
3. Exercise: The counting unit of 0.7 is (? One tenth? ), it has (? 7? ) such a counting unit.
0.04 has (? 4? ) 0.0 1, (? 0.9? ) consists of nine 0. 1
0.307 is made up of (? 3? ) one tenth and (? 7? One thousandth of the composition.
A number consisting of four tens, five ones and six tenths is (? 45.6? )
What is the number consisting of 1% and three thousandths? 0.0 13? )
(3) Decimal reading and writing:
1, decimal reading:
The integer part is read as an integer. The integer part of 0 is read as "zero", the decimal point is read as "point", and the decimal part reads the numbers on each digit in turn.
Such as: ①? Reading: 46.056 0.7754 Reading: 0.7754.
2. Decimal writing:
The integer part is written as an integer, the integer part is written as 0, the decimal point is written in the lower right corner of each digit, and the decimal part is written on each digit in sequence.
Example: ①? 89.74: 89.74 0.25 Writing: 0.25
Simulated test questions (answer time: 30 minutes)
1, fill in the blanks:
(1) The second digit to the left of the decimal point is (), and the third digit to the right of the decimal point is ().
(2) 15 0.0 1 Yes (), 24 0. 1 Yes ().
(3)0.08 has () one percent and 0.5 has () one percent.
(4) A decimal is composed of five thousandths and seven thousandths, and this decimal is ().
(5) The decimal point of 20.5 is moved two places to the left and then one place to the right. The decimal point should be ().
(6) Move the decimal point of a decimal to () by three places, and the decimal point will be reduced by () times.
(7) To enlarge a decimal by 100 times, just move the decimal point by ().
(8) Write in 0.057 () and in 10.654 ().
2. Judges:
(1) Add two zeros at the end of the decimal, and the size of the decimal remains the same. ()
(2) Rewrite 400,000 meters into tens of thousands of meters, which should be written as: 400,000 meters. ()
(3) Three decimal places must be greater than two decimal places. ()
(4) 95 kg =0.095 ton. ()
(5)0.5 means five tenths, and 0. 15 means fifteen tenths. ()
(6) One percent of 1 0 is one thousandth of1. ()
(7) One tenth is greater than one percent. ()
(8) Decimals are the same as integers, and the ratio between every two adjacent units is 10. ()
3.？ choose
(1)0.75 is one percent ()
A. 10 times? B. 75 times? C. 100 times
(2) The tenth 7 is the tenth ().
A. 10 times? 100 times
(3) The decimal number greater than 5 and less than 6 is ()
A. 10? Nine c's. I cann't count them
(4) Write a number, where thousands and one thousandth are 5, and other numbers are 0 as decimals ()
A.5500? B. 5.005C
Test answer
1, fill in the blanks
(1) The second digit to the left of the decimal point is (ten), and the third digit to the right of the decimal point is (one thousandth).
(2) 15 0.0 1 Yes (0. 15), 24 0. 1 Yes (2.4).
(3) The percentages of 0.08 and 0.5 are 8% and 50% respectively.
(4) Five ten thousandths and seven thousandths form a decimal, and this decimal is (0.507).
(5) The decimal point of 20.5 is moved two places to the left and then one place to the right. The decimal point should be (2.05).
(6) Move the decimal point of a decimal to the left by three places, and the decimal point will be reduced by (1000) times.
(7) To enlarge a decimal by 100 times, just move the decimal point to the right (two digits).
(8) in 0.057 (? 0.057? ), written in 10: 654 (? 10.654? )。
2. Judges
(1) Add two zeros at the end of the decimal, and the size of the decimal remains the same. (√)
(2) Rewrite 400,000 meters into tens of thousands of meters, which should be written as: 400,000 meters. (×)
(3) Three decimal places must be greater than two decimal places. (×)
(4) 95 kg =0.095 ton. (? √? )
(5)0.5 means five tenths, and 0. 15 means fifteen tenths. (? ×? )
(6) One percent of 1 0 is one thousandth of1. (? ×? )
(7) One tenth is greater than one percent. (? √? )
(8) Decimals are the same as integers, and the ratio between every two adjacent units is 10. (? √? )
Step 3 choose
(1)0.75 is one percent (? b？ )
A. 10 times? B. 75 times? C. 100 times
(2) The tenth seven is the tenth seven (? b？ )
A. 10 times? 100 times
(3) The decimal number greater than 5 and less than 6 is (? c？ )
A. 10? Nine c's. I cann't count them
(4) Write a number, where a few thousandths and a few thousandths are 5, and others are 0 as decimals (? c？ )
A.5500? B. 5.005C