Good friends1919,2828, hand in hand, 3737 is really close, and 4646 will go together. Make a pair of hands in half. Look at large numbers, divide them into decimals, make up ten, and add up the remainder. Remember large numbers in your mind and decimals in your hand. One plus nine, ten tadpoles, two plus eight, ten old ducks, three plus seven, ten old hens, four plus six, ten golden monkeys, five plus five, and ten big tigers. Think of 1 when you see 9, 2 when you see 8, 3 when you see 7, and 4 when you see 6.
When you see the big corner decimal system, switch the two numbers first. Minus nine plus one, eight plus two, seven plus three, six plus four, five plus five, four plus six, three plus seven, two plus eight, break large numbers and add decimals.
Song's recommendation is similar to the ten-point method:
1, mathematical symbol
Two numbers plus a plus sign, one horizontal and one vertical plus one, two numbers minus a minus sign, one horizontal minus one, two horizontal equals the sign, two butterflies plus one, two butterflies plus 1 equals three, three butterflies minus one, three minus 1 equals two, and plus or minus equals the sign. It is very important to calculate symbols.
2. Integer addition
Integer addition is regular, and the same digits should be aligned. And less than ten fell in the original position, and more than ten entered one. Go down for more than ten times, and add whichever one is dropped. Add up the carry, and the result is not less than half a cent.
3. Integer subtraction
Integer subtraction is regular, and the same numbers should be aligned. Reduce the time and difference greatly, and borrow less. Borrow once, subtract once, and add once. Add and subtract the results in the original position. Be careful when borrowing continuously, and remember what is left after borrowing.