Law of subtraction operation

(1) If you subtract several numbers from a number continuously, you can subtract the sum of all the subtractions of this number, and the difference remains unchanged, that is, a-b-c=a-(b+c).

(2) If a number subtracts two numbers continuously, you can subtract the second subtraction first and then the first subtraction, that is, A-B A-B-C = A-C-B C-B.

Law of division operation

(1) If a number is divisible by two numbers in succession, it can be divisible by the set of these two numbers, that is, a÷b÷c=a÷(b×c).

(2) If a number is divisible by two numbers in succession, it can be divisible by the second divisor first and then by the first divisor, that is, A ÷ B ÷ C = A ÷ C ÷ B

Law of product change: in multiplication, if one factor remains unchanged, another factor will be expanded (or reduced) several times, and the product will also be expanded (or reduced) by the same multiple.

Summary: One factor magnifies factor A, another factor magnifies factor B, and the product magnifies factor AB.

One factor subtracts one factor, another factor subtracts B, and the product subtracts AB.

Quotient invariance: in division, the dividend and divisor are expanded (or reduced) by the same multiple at the same time, and the quotient remains unchanged. m≠0a÷b=(a×m)÷(b×m)=(a÷m)÷(b÷m)

Generalization: the dividend enlarges (or reduces) a factor, and the quotient enlarges (or reduces) a factor, while the divisor remains the same. The dividend is constant, the divisor is enlarged (or reduced) by a factor, but the quotient is reduced (or expanded) by a factor.

By using the changing law of product and the invariant law of quotient, some calculations can be simplified. But pay attention to the remainder in the division with remainder. For example: 8500÷200= Divider and divisor can be reduced by 100 times at the same time, that is, 85472 =, the quotient remains unchanged, but the remainder 1 minus 100, then the original remainder should be 100.