Simple xpath

Hi,

I'm creating counters to show how many people signed up to use the service last month. The youngperson entity has a datejoined attribute. 

In the microflow that i'm using to count how many young people signed up i'm trying to write an xpath to filter the results to the people that joined last month with no luck.

I'm aware this is probably very simple i just haven't had to use xpath for this purpose before and could do with some advice.

Thanks

C