where is the other 325?!

I dont understand why 500 divided by 70 is 7.142857143...

why 3500, i divide by 70 and divide by 4, i get 12.50

but then, when i take 12.50 - 10= 2.50, and when i times it back, i dont get 500.. i get 175 instead.

where did the equation went wrong. where's the other 325? I've been looking for that stupid 325 for more than half an hour.. staring at that budget sheet like an idiot.. but.. i just.cant.get.it.right! >.<
3500-3000= 500 <-- this is the answer i want.

3500 divided by 70 = 50
50 divided by 4 = 12.50
12.50 - 10 = 2.50
2.50 x 70 = 175

gah! i dun understand! i bet i did something wrong SOMEWHERE but i just couldnt find it.. i'm so damn frustrated right now.. T.T

=) <-- what's with that smiley.. i'm SUPPOSE to be frustrated.. >.<

righttt.. you guys probably dont understand.. but who cares? i'm just spreading my frustration in my blog. btw, i KNOW i'm stupid.

btw, this has NOTHING to do with Maths or Add maths.. its just my stupid brain..