It is really one to ten. First of all, our writing hand is the right hand. Look, the single digits are on the right, right? Son, think about it. If I count tens of digits first, if I need to borrow single digits or borrow them for a period of time, do I have to count them again in ten digits? Is that an extra step? For example:+18 In this formula, if you first calculate the ten digits, you get 5+ 1=6, and then calculate the one digit-74, you get 6+8 = 65438. The correct way is to calculate the unit number first and get 6+8= 14, so the unit number is 4,5+1+1= 7 (the second1is the unit number), and the ten digits are 7. You can ask questions if you don't understand.