I've got to calculate whether some total charges are correct but the format
of the charges is not straight-forward.

It is based on a range ie.
1 = $100
2-10 = $75
11 - 20 = $50
21+ = $25

These charges are applied in steps. ie. if there is 11, the 1st will be
charged $100, the 2nd - 10th charged $75 each and the 11th charged $50.

What function can I use to indicate the total charges are correct with "OK"
"NOT OK"?

I am using a reference figure for the total number of products and another
reference figure for the total charges - to compare against.

Any one got any ideas??????

TIA