Thanks Richard. Fully understand. Each statement should be processed in turn. So if the statement is C=Round(C-C/10) then you should take the value C you have calculated fro the above statement and then basically remove 10% from it.

What I've done is attached a file containing how things should work.

Columns A/B/C are the inputs E/I/A. Column D is the value of C I should expect to see.

Column E is the result of 
C= (Ix8)+(Ax4)
Column F is the result of column E with this applied: 
round (C/4)
Column G is the result of Column F with this applied: 
If (C<250) then C=round ((C/250)x100)
If (C>250) then C=round ((250/C)x100)
If (C=250) then C= 100
Columns H, I and J perform the calculation of removing 10% depending on the value of E. J is the final figure I am calculating. 
If (E<11) then C=round (C-(C/10))
If (E<21) then C=round (C-(C/10))
If (E<31) then C=round (C-(C/10))
So I can do the calculation if I do it in stages, but not by writing a single formula. Maybe that is how I will have to do it?

It should be noted for the purposes of this exercise I am using the ROUND function and not the Bankers Rounding function(which is slightly different) I am using in my master spreadsheet hence the slight differences in the rounding.

Book1.xlsx