1, there are three hands on the clock face, namely hour hand, minute hand and second hand, of which the second hand is the fastest and the hour hand is the slowest. (The hour hand is the shortest and the second hand is the longest)

2. Measure for a short time, usually seconds. Seconds are smaller units of time.

The longest and thinnest hand on the clock face is the second hand. It takes 1 second for the second hand to walk a small square.

4. Stopwatch: generally used in sports to record time in seconds.

5. Common time units: hours, minutes and seconds.

6. Time units: hours, minutes and seconds, and the forward speed between every two adjacent units is 60.

1 hour =60 minutes 1 minute =60 seconds and a half hour =30 minutes and 30 minutes = half an hour.

7. The minute hand takes a circle and the hour hand takes a big grid, which is 1 hour. The second hand turns, and the minute hand occupies a small space. 1 minute.

8. To calculate a period of time, you can subtract the start time from the end time.

Unit 3 Measurement

1. In daily life, relatively few items can be measured in millimeters (mm), centimeters (cm) and decimeters (dm).

Large objects are usually measured in meters (m).

The relatively long distance is generally in kilometers.

2. The track of a sports ground is generally 400 meters 1 lap, and 1000 meters is 2 and a half laps.

3. 1 The thickness of coins, rulers, magnetic cards, buttons, keys and ID cards 1 min is about1mm. ..

4. When the length or required quantity of an object with a relatively short volume is relatively accurate, it can be measured in millimeters.

5. The length of each cell in the middle of1cm is1mm.

6. When calculating the length, you can only add or subtract the same length unit; When the units are different, they should be converted into the same units before calculation.

7. When expressing the weight of an object, mass units are usually used. The weight of lighter items can be measured in grams. According to the quality of general commodities, it is often taken as "kilogram"; Generally, "ton" is used to represent the mass or carrying mass of large objects.

8. Common length units: meter, decimeter, centimeter, millimeter and kilometer.

9. Length units: meters, decimeters, centimeters and millimeters, and the forward speed between every two adjacent units is 10.

1 m = 10 decimeter, 1 decimeter = 1 0cm,1cm =10mm.

1m = 100cm 1km(km)= 1000m

10, mass unit: tons, kilograms and grams, and the forward speed between every two adjacent units is 1000.

1 ton = 1 000kg1kg =1000g

Addition and subtraction in the second and fourth units

Number of digits and minimum digits of 1:

One digit of is 9, and the minimum digit is 0.

The two digits of are 99, and the smallest two digits are 10.

The three digits of are 999, and the smallest three digits are 100.

The four digits of are 9999, and the smallest four digits are 1000.

The five digits of are 99999, and the smallest five digits are 10000.

The three digits of are less than the smallest four digits 1.

2. When adding and subtracting with a pen: the same numbers should be aligned; From the number of units. When the number on which bit adds up to 10, go to the previous bit and input1; Where the number of digits is not reduced enough, take 1 from the previous digit as 10, and then reduce it after adding the standard; If the previous digit is 0, it is 1 of the previous digit.

3. Sum of two three digits: it may be three digits or four digits.

4. Addition formula:

Appendix+Appendix = Sum

And-another addend = addend

5, subtraction formula:

Negative-negative = difference

Difference+subtraction = subtraction or subtraction = difference+subtraction

Negative difference = negative

6. When calculating orally:

Example: (1)35+48, first 35+40=75, then 75+8=83.

(2)72-28, first 72-20=52, then 52-8=44.

Or 72-30=42, and then 42+2=44.

7. When the words "about", "about", "estimate", "estimate" and "should be prepared" appear in the question, they are all estimates.

Unit 5 Understanding

How many times is one number more than the other? Calculate by division: one number ÷ another number = multiple.

How many times is 36 4? 36÷4=9

Suppose a number is several times that of A, and find this number. Calculate by division: A÷ multiple = this number.

As we all know, the multiple of 5 of a number is 35. How did you find this number? 35÷5=7

What is the multiple of a number? Multiplication calculation: a number × multiple = result.

How much is six times nine? 9×6=54

Unit 6 multiplies a number by a number.

1, how to write multiple digits multiplied by one digit (carry):

For the alignment of the same number of digits, each digit of multiple digits is multiplied by one digit in turn from the unit number. If the product of the best digit is more than several tens, it is multiplied by the previous digit.

2. In multiplication, multiplier is also called factor.

Multiply 3, 0 and any number to get 0; Multiply 1 by any number except 0 to get this number.

4. Three digits multiplied by one digit: the product may be three digits or four digits.

Unit 7 Rectangular and Square

1. When a small square is used to form a rectangle or a square, the shorter the length and width (or the same length and width), the shorter the circumference.

2. Features of quadrilateral: It has four straight sides and four corners.

3. The characteristics of a rectangle: the opposite sides are equal and there are four right angles.

4. Features of a square: all four sides are equal and there are four right angles.

5. The length of a closed figure is its circumference.

6. Perimeter of rectangle = (length+width) ×2 Perimeter of square = side length ×4

7. Cut out a square in a rectangle, and the width of the rectangle is the side length of the square.

A preliminary understanding of the score in Unit 8

1, the meaning of score: divide a whole into several parts on average, and the number representing 1 or several parts is the score.

Representative: Divide a whole into five parts on average, and take two of them.

Representation: divide a whole into four parts on average and take one of them.

2. The method of comparing sizes:

The numerator of (1) is the same, and the score with smaller denominator is larger.

(2) The denominator is the same: the larger the numerator, the greater the score.

3. Add and subtract fractions with the denominator. The denominator remains the same, and only the numerator is added and subtracted.