18 - 9 = (10 + 8) - 9 , (1 in the tens column, 9 in the units column)
= (10 - 9) + 8 , (addition and subtraction are done at the same time)
= 1 + 8 , (10 - 9 = 1)
= 9
Well- there’s always fingers and toes or physical counting. But yeah- where math doesn’t seem to work is usually where there is insufficient understanding of math or the operations needing to be applied.
There are easier way man.Your way is like trying to solve polynomial time problem with non-polynomial time algorithm,althought it work, it cost a lot of resources such as runtime, amortized timeand etc. and in this case your brain power.
= (10 - 9) + 8 , (addition and subtraction are done at the same time)
= 1 + 8 , (10 - 9 = 1)
= 9