Lattice algorithm, also known as "carpet laying", is a mathematical algorithm discovered in Italy more than 500 years ago. Later, it was introduced to China at the same time as the pen calculation in the Ming Dynasty. This algorithm needs to be calculated one by one and then added.

Let's take 46×75 as an example. What we do is to divide it into four formulas: 40×5, 6×5, 40×70 and 6×70, and get 200, 30, 2800 and 420 respectively, and then add up all the numbers to get 3450. So many formulas are worked out one by one with calculation funds, and then added together, which is slow and easy to write.

Simplified method

There is a simplified method. The first factor on the square is 46, and the second factor on the right is 75. Then write the product of every two numbers in their corresponding squares, such as 6×7=42, write 4 in the upper left corner of the square in the upper right corner, and write 2 in the lower right corner of the square.