I'm a very simple person with basic math knowledge. Recently I run into huge problems when calculating how much I spent.
Sometimes to calculate how much I spent I do a calculation $final sum - start sum$. However at other times I do $start sum - final sum$.
When I take the absolute values, are these two values guaranteed to be equal? I've noticed sometimes when I do it one way, or the other way, I get different numbers. Is it because I made a mistake entering the numbers or it's not guaranteed that absolute values are equal?
Somehow I can't reproduce this error today but I just ran into it yesterday. When I did $start sum - final sum$ I got value $y$, but when I did $final sum - start sum$ I got value $z$. I forgot to write down the numbers.
The best way to answer this might be to pick two arbitrary values for your starting sum and your final sum.
So, let $X=startsum$ and $Y=finalsum$
Now, let $x$=100 and $y$=175
$$x-y=-75$$ $$y-x=75$$ $$|-75|=75$$
So you see, any discrepancy between the absolute values of x-y and y-x must be some input error on your part.