The homotopy of two numbers, such as 23 and 27, is the homotopy of the head. When calculating, take 23 and 27 as examples. The product of the number on the decimal place of 23×27 = 10 (the number on the decimal place plus 1)+ the number on the two digits is here.
In the past, ten was the tail, for example, 46, 66 was the tail of the previous ten. When calculating, take 46,66 as an example, 46× 66 =10 (4+1)× (10× 6)+6 2 = 3036.