If I have a figure to which I have to apply an additional 17.5% say $100 so
that it eqals $117.5. What formula do I use to work out what the original
starting price was when I am confronted by $117.50 ie I want to get back to
the $100 figure. So in this case 17.5% up is what formula to go down and
what is the rule for going down from an number.

Hope this clear and much thanks.

Eqa