Summary of fifth grade mathematics knowledge
1, decimal multiplication integer (p2,3): meaning-a simple operation to find the sum of several identical addends.
For example, 1, 5×3 indicates how many times 1, 5 is or the sum of three 1, 5.
Calculation method: first expand the decimal into an integer; Calculate the product according to the law of integer multiplication; Look at a factor * * *, how many decimal places there are, and count the decimal points from the right side of the product.
2. Decimal times decimal (P4, 5): that is, what is the score of this number.
For example, 1, 5× 0,8 is eight tenths of 1, 5.
1, 5× 1, 8 is how many times 1, 5.
Calculation method: first expand the decimal into an integer; Calculate the product according to the law of integer multiplication; Look at a factor * * *, how many decimal places there are, and count the decimal points from the right side of the product.
Note: In the calculation results, the 0 at the end of the decimal part should be removed to simplify the decimal; When the number of decimal places is not enough, use 0 to occupy the place.
3. Rule (1)(P9): The product of a number (except 0) multiplied by a number greater than 1 is greater than the original number.
A number (except 0) is multiplied by a number less than 1, and the product is less than the original number.
4. There are generally three methods to find the divisor: (P 10)
(1) rounding method; (2) into law; (3) Tailing method
5. Calculate the amount of money, and keep two decimal places, indicating that the calculation has reached the point. Keep one decimal place, indicating that the angle has been calculated.
6. The operation of (p11) four decimal places is the same as that of an integer.
7, operation law and nature:
Addition: additive commutative law: a+b=b+a Addition Law: (a+b)+c=a+(b+c).
Subtraction: Subtraction property: A-B-C = A-(B+C) A-(B-C) = A-B+C.
Multiplication: multiplication commutative law: a× b = b× a.
Law of multiplicative association: (a×b)×c=a×(b×c)
Multiplication and distribution law: (a+b) × c = a× c+b× c (a-b) × c = a× c-b× c.
8. Significance of fractional division: Know the product of two factors and one of them, and find the operation of the other factor.
For example, 0,6 ÷ 0,3 means the operation of finding another factor by multiplying two known factors 0,6 and one of them 0,3.
9. Calculation method of decimal divided by integer (P 16): decimal divided by integer and then divided by integer. The decimal point of quotient should be aligned with the decimal point of dividend. The integer part is not divided enough, quotient 0, decimal point. If there is a remainder, add 0 and divide it.
10, (P2 1) The calculation method of division in which the divisor is a decimal number: first expand the divisor and the dividend by the same multiple to make the divisor an integer, and then calculate according to the rule of fractional division in which the divisor is an integer.
Note: If there are not enough digits in the dividend, make up the dividend with 0 at the end.