Sum expression based on >date

[#1]

Hi I have the following expression

=Sum(all if (DateMonth >= Date('10/11/08'),sales)/Sum(all if(datemonth >= date('10/11/08'),Purchases)

however it isn't returning anything, anyone got any ideas what is wrong with the expression.

Thanks in advance

[#2]

Hello,

I dont think you need the all in the statement

=Sum(if (DateMonth >= Date('10/11/08'),sales)/Sum( if(datemonth >= date('10/11/08'),Purchases)