1, can you write three numbers as hundreds plus dozens, or hundreds plus dozens plus several, and multiply them by one number respectively, for example:

123x4

=( 100+20+3)x4

= 100x4+20x4+3x4

=400+80+ 12

=492

2. Three digits can be written as whole hundred plus one or whole hundred minus one, respectively multiplied by one digit, for example:

203x3

=(203+3)x3

=200x3+3x3

=600+9

=609

Calculation rules of multiplication:

Number alignment, starting from the right, multiply the first factor by the number on each bit of the second factor, and the end of the number will be aligned with which bit of the second factor.

1, the digit is 1. Two-digit multiplication method: the number of digits of the multiplier is added to the multiplicand, and the number is the front product, and the number of digits of the multiplier is multiplied by the number of digits of the multiplicand, and the number is the back product, full ten and the first.

2. Multiplication method of a two-digit number with the unit of 1: multiply by ten digits, the number is the previous product, and the number is added with ten digits. Then write the number, and finally add 1.

3. Multiplication method of two-digit numbers with the same ten digits but different digits: Multiplied by the multiplier digits, and then multiplied by the integer of ten digits, the product is the former product, and the single digit multiplied by the single digit is the latter product.