If you don’t see a difference between “do the tens, then do a simple subtraction with digits between 1 - 9” and dividing an arbitrary number by four, then there is no sense arguing. Also it would lead to bad results in your example - the average number of legs a sheep has isn’t 4.
Works for someone born in 1980 like myself. Easy to track when born at the beginning of a decade.
I mean, equally as easy to split the equation. Born in 1999? Subtract current year from 1990. Then subtract 9. Easy.
And the easiest way to count sheep is to count all the legs and divide by 4, right?
If you don’t see a difference between “do the tens, then do a simple subtraction with digits between 1 - 9” and dividing an arbitrary number by four, then there is no sense arguing. Also it would lead to bad results in your example - the average number of legs a sheep has isn’t 4.
For most herds of sheep, the average is four.