1 1-7= 1 1-9= 12-3= 17-9= 13-8= 13-5= 12-9= 16-7= 14-8= 12-6= / kloc-0/4-9= 12-7= 1 5-6= 15-9= 14-7= 12-8= 1 1-3= 13-9= 17-8= 1 1-6=
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1, counting method
Count them one by one by hand or by drawing dots.
2. Relationship
It's basically a counting method, just counting one by one on the basis of the first number. For example, 8+5, the first number 8 does not need to be followed by the number 8+1+1+1.
3. Two-handed symbol
Poor students can use the "two-handed memory method" to help. One hand represents a number, the thumb represents 5, and the other four fingers each represent 1. For example, 8+5, put your hand out as required, and you will know at a glance that 8+5= 13. After regular practice, students can see the formula, that is, present the shape of the hand in their minds, and with the help of the shape, students can calculate the numbers immediately. This can also be said to be a simple mathematical model.
This is different from counting fingers, which is a low level, while the "two-handed memory method" belongs to group calculation and reaches a higher level.
4, abacus mental arithmetic
It is a new algorithm combining abacus calculation and mental calculation, which was founded by Mr. Chen, a math educator in his 80s. Its basic method is to calculate by hand code. The thumb of the right hand stands for 5, each finger of the rest stands for 1, and each finger of the left hand stands for 10. Use your mouth, heart and brain to calculate.
5. Add up to ten methods.
8+5=8+2+3= 13, decompose the second addend and multiply the first addend by ten.
6. Formula method
On the basis of understanding the method of adding ten, memorize the formula of addition and directly report the result 8+5= 13.
7. Several methods of abdication subtraction within 20 years.
Take 13-9=4 as an example:
(1) "counting method"
Children are likely to be 13 subtracted one by one, leaving 4 after subtracting 9. This algorithm is the most primitive and basic method. It is based on the fact that children have learned to count below 20, and some children will achieve the purpose of "subtraction" by "counting". At first, children can use this number method when they are in contact with abdication, but in the future, they should gradually practice it, realize that other algorithms are faster and simpler, and choose a more optimized method when calculating.
(2) "Breaking Ten Laws"
13 consists of 1 tens and 3 ones. You can subtract 9 from 10 and combine the remaining 1 with 3 in the unit to get 4 1. The basis of this algorithm is that children have mastered the composition of 1 1~20, and can calculate the addition and subtraction within 1, including the mixed operation of addition and subtraction.