If you're selling for £100 PLUS VAT, the VAT is £17.50 so total customer pays is £117.50.
17.5% VAT content in £100 is £14.89 not £17.50. ie [roughly] £85.11 + 17.5% VAT = £100.
HTH
Last edited by Paddy; Apr 8, 2010 at 02:07 PM.
Reason: edited to make clearer