Basic Subtraction 3

L.I, to add numbers by making tidy numbers,Today I was learning about tidy numbers.Tidy Numbers are numbers that end with a 0 like 10,20,30,40. Insted of doing additions I done subtractions.For example 17-8=?,With find the lowest number which is 8 and then add 2 to the 8 which would make 10 and then add another 2 to the 17 which would make 19 add those numbers together which would make 19-10=9.It was hard figuring out the numbers on the basic subtraction 3