9X 10=90 yuan.

This is the problem of the first volume of the second day of junior high school. I only learned 9×9, but the children don't understand 9× 10. It should be 10- 1=9 (m) 9×9=8 1 Yuan 8 1+9=90 yuan.

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 digits 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 front product, and the single digit multiplied by the single digit is the back product.