A number multiplied by two one-digit numbers can be rewritten as the product of this number multiplied by these two numbers according to the situation, which makes the calculation simple.

Example:

Calculation: 19×4×5

19×4×5

= 19×(4×5)

= 19×20

=380

When calculating, adding a bracket can make the calculation simple. Because there is a multiplication symbol in front of the brackets, there is no symbol in the brackets.

Second, the decomposition method

A number multiplied by a two-digit number can be decomposed into two one-digit multiplication forms according to the situation, and then this number is multiplied by two one-digit numbers continuously, so the calculation is simple.

Example:

Calculation: 45× 18

48× 18

=45×(2×9)

=45×2×9

=90×9

=8 10

Decompose 18 into 2×9 form, and then remove the brackets to make the calculation simple.

add

A, Integer and Decimal: the same digit is aligned, starting from the low digit and full decimal into one.

B. Fractions with the same denominator: numerators with the same denominator are added. Fractions with different denominators: divide first, then add.

subtraction

A, Integer and Decimal: the same digits are aligned, decreasing from the lower digit, and then decreasing if the digits are not decreased enough.

B, the denominator score is the same: the denominator is unchanged, and the numerator is subtracted. Denominator score: divide first, then subtract.

increase

A. Integer and Decimal: Multiplied by the number on each bit of the multiplier, with which bit the last bit of the number will match. Finally, add the product, the factor is decimal, and the decimal places of the product are the same as those of the two-digit factor.

B. Fraction: The product of numerator multiplication is numerator, and the product of denominator multiplication is denominator. The first reducible result should be simplified.

separate

A, Integer and Decimal: How many digits are there in the divisor? Look at the first few digits of the dividend first (if it is not enough, look at one digit), and write the quotient on which digit other than the dividend. Dividers are decimals, which are first converted into integers and then divided by them. The decimal point of quotient is aligned with the decimal point of dividend.

A divided by B (except 0) equals the reciprocal of A divided by B. ..