There are several ways to multiply two-digit numbers:
1.The ten digits that fit into both multipliers are both 1s.
For example: 15*17=255
Calculation process: (15+7)*10+5*7
First, use the multiplier 15, add the single digit of the multiplier 17, add 0 to the end of the number, become 220, and then multiply the single digit of the two multipliers to get 35, and finally add the two results to 255.
2.The single digit that fits both multipliers is 1. First, multiply the tens of the two multipliers, then add the tens of the two multipliers, and finally, multiply the two single digits 1 and 1 to get 1, and add the 3 results to get the product.
For example: 41 x 51 = 40 x 50 + 40 + 50 + 1 = 2091
3.It is suitable for two-digit multiplication with the same ten digits but different single digits. Use the first multiplier, add the unit of the second multiplier, and then multiply by ten digits 70 to get 5600;Next, multiply the two single digits to get 16, and add it to the previous result of 5600 to get the final product of 5616.
Example: 21*27=(21+7)*20+7=567
The above method is not an oral calculation
General Law: How to find: ab*cd
You can simplify the complex, a0*cd+b*cd, or replace the ten digits with the same.
For example: 27 x 36 = 27 x (26 + 10) = 27 x 26 + 270 = (27 + 6) x 20 + 42 + 270 = 972
Although the formula may seem long, it will be much easier to calculate after becoming proficient)).
Of course, it can also be simplified as: 27 * 36 = 27 * 30 + 27 * 6 = 972
The above are several quick calculation methods for two-digit multiplication, I hope it will be helpful to you.