SOQL IN String Literals

Snap: Salesforce SOQL

If I hard code it, it works. 

SELECT ConversionRate, CreatedById, CreatedDate, Id, IsoCode, LastModifiedById, LastModifiedDate, NextStartDate, StartDate, SystemModstamp FROM DatedConversionRate 

   where IsoCode in('AUD','CAD','EUR')

 

But If I pass the IsoCode values in a variable it does not work. What am I doing wrong here? Please see the screen shots attached.