Multiplication can be found by division:11788 ÷ 421= 28 or11788 ÷ 28 = 421.
Extended data:
Four problems in vertical calculation of multiplication;
1, the last digit of two numbers should be aligned.
2. Write as many numbers as possible above, and write as few numbers as possible below to reduce the times of multiplication.
3. If there is a "0" at the end of both numbers, the last digit of the number can only be aligned before the "0" when writing vertically, and finally the number "0" owned by the two numbers after vertical product is added.
4. Decimal multiplication should determine the position of the decimal point of the product according to the multiple of the decimal.