This formula table1* * 20 contains all addition calculations in which the sum of two one-digit numbers is two digits within 20. Note: First of all, each formula has two addition formulas. For example, if 92 is 1 1, we can calculate 92 =1,29= 1 1, so we can use the properties of additive commutative law to calculate the addition formulas of other commutative addends.
First-year students now know the truth of addend exchange position and invariance. Except 99 18, 88 16, 77 14, 66 12. Second, the addition number in the formula is expressed by chinese numerals, and the result is expressed by mathematical figures, which helps students to distinguish.
92 1 1 means that the table addends are 9 and 2, and the result is 1 1. Thirdly, in the process of oral arithmetic training, students can deepen their memory in various ways and form conditioned reflex. For example, recite, answer grades, fill in the blanks, and do oral calculations regularly.
The requirements for timing and oral calculation are roughly as follows: the first category is addition and subtraction without carry within 10 and addition and subtraction within 10; the second category is addition of 20 with carry, addition of more than 10 without carry and subtraction of more than 10 without abdication. During the test, each exit has 120 questions classified. The number of questions that can be completed in 5 minutes is the evaluation standard of students' performance. The first-class passing standard is 70-80 questions, and the excellent standard is 90- 100 questions.
There are 60-70 questions on the second-level passing standard and 80-90 questions on the excellent standard. In a word, oral arithmetic training, especially the oral arithmetic of carry addition within 20 is the basis of future calculation, and the abdication subtraction within 20 to be learned in the second book is developed on this basis. It is the most important thing to cultivate students' computing ability.
Counting fingers and sticks can't be called real calculation, only ordinary numbers, and can be called real calculation with the method and formula of "rounding off ten".
Children are also required to achieve a certain calculation speed on the basis of accuracy, that is, correct and fast! I hope parents can think of some ways, such as making dictation cards, listening and calculating at ordinary times, applying dictation in daily life and doing some dictation exercises to train their children's computing ability and develop their thinking level.
Especially at present, children's school age is generally small and their computing ability is weak. Let's work together to make every child in the class feel the fun of learning mathematics as soon as possible!