I've recently taken on some bookkeeping work from an accountant. One of the clients he has passed on to me doesn't have copies of any sales invoices so i've been told by the accountant that all sales receipts are to be treated as net plus 20% as CIS gross receipts. Thats all fine, i know the double entry for this but i'm having a bit of a no brainer moment when working out what the gross figure would of been before the CIS was deducted! Say for example £300 was received into the bank account which is the net amount, from this how would i work out the amount of CIS which would of been deducted?