Calculating kg per box with loss He I am not to good in math but I have a situation I need to calculate.
Sorry if this looks stupid I really doubt my self if it comes to calculating numbers.
I have the following numbers:


*

*gross kg: 100kg

*loss due to production: 2kg per box

*invoice kg: 8kg per box


Now I need to know how many boxes I can fill 
Found the answer:
-------------------------------------
| raw | kg/box | los kg/box | total |
-------------------------------------
| 100 |   8kg  |    2kg     |  10kg |
-------------------------------------

How many boxes can I fill calculation:
100 / 10 = 10
8 X 10 = 80
chek 10 X 10 = 100 minus is trash 100 - 80 = 20
Now I have 80kg left and I can put this in:
80 / 8 = 20 20 boxes of 8kg
cheksum:
10 X 10 = 100
10 X 8 = 80
10 X 2 = 20
80 + 20 = 100
So the final numbers are:
---------------------------------------------
| raw | trash |  leftover  | boxes with 8kg |
---------------------------------------------
|100kg|  20kg |    80kg    |       10       |
---------------------------------------------

In the end it was really easy an logic but I am dyslexic. I find it hard to calculate in my head so I have to write everything on paper. Sometime taking very long time for simple questions. 
 A: The simple way to solve this is to say that in order to fill one box, you need 10 kg of produce, of which 8 kg will go into the box and 2 kg onto the floor. With 100 kg in all, you can fill 100/10 = 10 boxes.
The problem with your calculation is that you are trying to determine the total waste before you know the total number of boxes. Your first number 12.5 is the number of boxes you would be able to fill if there were no waste. Your second number 25 (kg) is the total waste if you fill 12.5 boxes. In reality, you will not be able to fill 12.5 boxes because of the waste, so the total waste will be less than 25 kg. Hence you will not get the right answer when you use the number 25 kg in your calculations. 
A: It's not very hard, but I'm not english, so maybe I misunderstood gross, invoice,..
I don't understand how you checked your solution either ^^
What you already know
Raw materials: 100kg
Box contents: 8kg
Lost per box: 2kg
Easy way
$\frac{raw}{\frac{raw}{box}} = \frac{100kg}{8kg+2kg} = 10$ boxes
Percentage solution
$\eta = \frac{8kg}{8kg+2kg} =  0.8 = 80\%$
$\eta \cdot 100kg = 80kg$
$n = \frac{80kg}{8\frac{kg}{box}} = 10$ boxes
