1, the writing method of multiplying two digits by two digits, first multiply the digits of three digits from low to high, and the end of the product is aligned with the digits of two digits; Then multiply the numbers on each bit of the three-digit number from low to high in turn, and the end of the product is aligned with the ten digits of the two-digit number; Finally, add the products of the two multiplications.

2. Statistical table: Fill in the statistical table according to the relevant data of the survey, and fill in the corresponding data in the corresponding column. The total is the sum of the statistics of each category. When collecting and sorting data in sections, you can sort out a set of data in sections according to the actual situation. When collecting and sorting data in sections, you can use the method of drawing "positive".

3. Bar chart: When making a bar chart, you can determine how many units 1 stands for according to the size of the number, and determine the horizontal and vertical axes. Features: Bar charts can visually display the quantity.

4, the operational nature of subtraction, a number MINUS two numbers is equal to the sum of this number MINUS these two subtractions. Expressed in letters: ab-c=a-(b+c) The operational nature of subtraction, the sum of one number minus two numbers is equal to each addend in this number minus the sum continuously.

5. Use the multiplication algorithm for simple calculation. In the multiplication calculation, when the product of two multipliers is exactly an integer of ten, one hundred and one thousand, the calculation can be simplified by using the multiplication algorithm. By using the method of decomposition, a multiplier is decomposed into the form of multiplication of several numbers, so that this multiplier is the product of other multipliers. Multiplication and division: multiplication and division equals division and multiplication.

6. Operational nature of division: A number divided by two numbers in succession (divisible every time) is equal to the operational nature of the product of this number divided by these two divisors, and the product of a number divided by two numbers is equal to the number divided by each multiplier in this number's continuous product.