I. About synthesis (or synthesis):

"1 plus 4 equals 5", just put a stick. There are 1 on the left and 4 on the right. Put them together to form a pile, which is 1+4 = 5 or 4+1= 5; So "combination" is "addition".

Similarly, "2 plus 3 makes 5", there are 2 sticks on the left and 3 sticks on the right. If you put them together and pile them up, you will get five sticks, which is 2+3 = 5 or 3+2 = 5.

Second, divided into

"5 can be divided into 1 and 4" to put small sticks: take out 1 from five sticks and leave four squares, that is, divide five sticks into two piles, one pile is 1 and the other pile is 4, so 5- 1 = 4, or 5-.

Similarly, "5 can be divided into 2 and 3" means that 2 sticks are taken out of 5 sticks and put aside, leaving 3 squares, that is, 5 sticks are divided into two piles, one pile is 2 sticks and the other pile is 3 sticks, so 5-2 = 3, or 5-3 = 2. So the action of "division" is the process of "subtraction".

Third, application

Skillfully divide and synthesize numbers within 10, and then smoothly calculate them in carry addition and abdication subtraction.

For example: 8+5 =? Think: Because 8 and 2 make up 10, we divide 5 into 2 and 3. First, add 8 to the divided 2 to get 10, and add the remaining 3 to get 13, so 8+5 = 13. It can be seen that in the calculation process of carry addition, division and synthesis of numbers are inseparable. Subtraction of abdication is also inseparable from division and synthesis of numbers.