Who knows a question or method for a 5th grader to practice speed arithmetic! 20

Unit 1:

1. Oral arithmetic (12 points).

2. Short arithmetic questions (6 points).

3. Calculation questions (6 points for each question, 12 points in total) 1 3－

1. Oral arithmetic (12 points).

2. Short arithmetic questions (6 points).

Unit 1: 1. Oral arithmetic problems (12 marks).

2. Short arithmetic questions (6 points).

3. Calculation questions (6 points for each question, 12 points in total) 1 3－

1. Oral arithmetic (12 points).

Example 1: Calculation:

Solution: The addition in the equation does not seem to be able to be calculated using the simple calculation method learned in math class, but each of these numbers only needs to be increased a little to become a whole number.

10. Whole hundred or whole thousand, after "rounding" these numbers, it will be easy to calculate. Of course, remember that how much you add when you "round up" is subtracted.

Example 2: Calculation: 1

Solution: The number of the formula starts from 1 and decreases sequentially until the last number is, so there are 100 numbers in the formula and the operation in the formula is to add two numbers and subtract two numbers, add two more numbers, subtract two numbers, and ......In such order.

Since the arrangement of numbers and the arrangement of operations are very regular, according to the rules, it can be considered to add parentheses to a group of every 4 numbers, and is there a certain rule in the operation results of each group of numbers? It can be seen that the first number in each group of numbers is subtracted from the third number, and the second number is subtracted from the fourth number, and each number is obtained, and the sum is, then, the result of the operation of each group of numbers (i.e., each parentheses) is that the whole equation of 100 numbers is exactly divided into 25 groups, and its result is the sum of 25.

1. If you can flexibly use the law of the exchange of numbers, you can also add brackets to the following grouping:

1 Example 3: Calculation:

Solution: The arrangement of the numbers of this equation is like a series of equal differences, but if you look closely, it is actually composed of two equal difference series, which is the first equal difference series, and each of the following numbers is more than the previous number, but the second equal difference series, and each of the following numbers is more than the previous number, so it should be divided into two segments and calculated according to the method of summing the equal difference number series.

== Example 4: Calculation:

Solution: One of the two factors in the equation expands by 10 times, and the other factor shrinks by 10 times, and the product remains unchanged, that is, this multiplication can be changed to 99; It can be divided into sums, so that after the change, the calculation is relatively simple.

Example 5: Calculation:

Solution: Although the two multiplication calculations in the equation do not have the same factor, but the numbers of the two numbers of the previous multiplication and the latter multiplication are the same, but the position of the decimal point is different.

= Solution: Although several numbers in the equation are a series of equal differences, the equation is not summed, and the result of this equation cannot be calculated by the method of summing the series of equal differences.

Students who usually pay attention to the accumulation of calculation experience may notice that the product of multiplying these three numbers with 13 is 1001, and a three-digit number multiplied by 1001, as long as the three-digit number is written twice in a row is their product, such as 578 1001 = 578578, this problem refers to this method to calculate, can skillfully calculate the correct number.

36x（70+6）=2376

The method of calculating the addition of any number of digits is very simple, and the learner only needs to memorize a general formula for addition and quick calculation - the addition of the base (for the number of carries) subtract and add supplement, and the addition of the front digit plus one "can completely solve the addition of any number of digits from the high number to the low digits, and the subtraction quick calculation method for calculating any number of digits is also the same as a general formula for subtraction and quick calculation - subtraction (for the number of borrowed digits) Addition and subtraction, subtraction of the previous phase minus one " It can completely solve the subtraction quick calculation method of any number of digits from high to low digits.

=71-（

41 The most authentic five-year calculation.