The abacus mental calculation formula represents an algorithm invented on the basis of calculation, which is suitable for abacus calculation. With the progress of the times, predecessors have summed up various abacus mental calculation formulas to facilitate people to calculate faster. According to the needs of addition, subtraction, multiplication and division in calculation, abacus mental arithmetic formulas can be divided into addition formula, subtraction formula, nine regression formula, regression formula and ninety-nine formula, among which ninety-nine formula is the familiar ninety-nine multiplication table.
1, addition formula
One up one, two up two, three up three, four up four, five up five, six up six, seven up seven, eight up eight, nine up nine; Two drops five to three, three drops five to two, and four drops five to one;
One to nine, two to eight, three to seven, four to six, five to five, six to four, seven to three, eight to two, nine to one.
2. Subtraction formula
One, two, two, three, three, four, five, six, seven, seven, eight, nine, nine; One on four to five, two on three to five, three on two to five, four on one to five;
One retreats nine, two retreats eight, three retreats seven, four retreats six, five retreats five, six retreats four, eight retreats two, nine retreats one.
3, except songs.
As soon as I get home, I will be ten when I see one.
Twenty-one equals five, every two equals ten, four equals twenty, six equals thirty and eight equals forty.
Three, one, three, two, six, twelve, ten, six, twenty, nine, thirty every Wednesday.
Four, one, two, four, two add up to five, four, three, seven, twelve, every four into ten, eight into twenty.
Double five times, five into ten.
Six-one plus four, six-two-three-twelve, six-three plus five, six-four-six-four, six-five-eight-two, six into ten.
Seven one plus three, seven two plus six, seven three four twelve, seven four five fifteen, seven five seven, seven six eight fourteen, every seven into ten.
Bayi plus two, 82 plus four, 83 plus six, 84 plus five, 8562, 8674, 8786, every eight into ten.
Nine goes with you, and every nine goes into ten.
4, nine return formula
Once (divided by 1): every one goes in, every two goes in, every three goes in, every four goes in, every five goes in, every six goes in, every seven goes in, every eight goes in and every nine goes in.
Two returns (divided by two): every two into one, every four into two, every six into three, every eight into four, 2 1 plus five.
Three returns (divided by three): three into one, six into two, nine into three, three into one, three into two.
Four returns (divided by four): every four into one, every eight into two, four and two phases add up to five, four and one are greater than two, and four and three are greater than two.
Five cycles (divided by five): every five cycles into one, 5 1 cycle is two, 52 cycles is four, 53 cycles is six, and 54 cycles is eight.
Six returns (divided by six): every six enters one, six three adds five, six one adds four, six two three leaves two, six four leaves four and six five eight leaves two.
Seven returns (divided by seven): every seven enters one, seven plus three, seven plus six, seven plus four, seven plus five, seven plus seven plus seven plus eight, seven plus four.
Eight returns (divided by eight): every eight enters one, 84 adds five, 8 1 adds two, 82 adds four, 83 adds six, 856 is greater than two, 867 is greater than four, and 878 is greater than six.
Nine returns (divided by nine): every nine returns to one, nine returns to one, ninety-two returns to two, ninety-three returns to three, ninety-four returns to four, ninety-five returns to five, ninety-six returns to six, ninety-seven returns to seven and ninety-eight returns to eight.
5. Formula of return business
Nothing but retreat, nothing but retreat, and two, nothing but retreat.
No return four, no return five, no return six.
No return 7, no return 8, no return 9.
9. Business Nine Formula
See no score 9 1, see no score 92, see no score 93.
See four division is 94, see five division is 95, and see six division is 96.
Don't divide 97 by seven, 98 by eight, and 99 by nine.
If all frogs, you should eat pests every day:
25*20=500 (piece)
Actually eat 620 a day, forget it:
620-500= 120 (piece)