Look at large numbers, divide them into decimals, make up ten, and add up the remainder.
Clap your hands, children. Let's sing ten songs.
One equals nine and two equals eight.
Three equals seven and four equals six.
Fifty-five adds up to ten.
2. Make up ten formulas
19 19 good friend 1 9
2828 hand in hand 2, 8
Three, seven, three, seven are so close.
Four four six four six.
5555 1 hand 5,5
Remember large numbers in your mind and decimals in your hand.
3. Subtraction breaks the formula of ten methods
Minus nine plus one, subtract eight plus two.
Minus seven plus three, subtract six plus four.
Minus five plus five, subtract four plus six.
Subtract three plus seven, subtract two plus eight.
Extended data:
Algorithm skill
add
1, two numbers add to keep the number unchanged: if one of the two added numbers increases, the other decreases, one increases and the other decreases.
When two numbers are added, one of them remains the same. If another number changes, this number will also change, and the result will change as much as the addend.
3. Add the two numbers and exchange positions to get the same number.
subtraction
1, one number subtracts another number, keeping the reduction unchanged: if the minuend increases, the result also increases, and the result increases as much as the minuend increases; When the minuend is reduced, the result is also reduced, and the result is also reduced by how much the minuend is.
2. Subtract one number from another to keep the minuend unchanged: if meiosis increases, the result will decrease, and the result will decrease as much as meiosis increases; If meiosis decreases, the results increase, and the results increase by how much meiosis decreases.
3. Subtract one number from another and keep this number unchanged: the minuend will increase as much as it increases; As much as the minuend is reduced, the minuend will also be reduced.
Baidu encyclopedia-four operations
Baidu encyclopedia-mental arithmetic