Days of a date

Hi Guys,
1- is there any option in xls form in calculation field to calculate the days of a date. like i want to calculate the duration between these to fields:
2- how can i let number to appear in percentage?
I mean if people inter 40 i want it to appeared 40%

See decimal-date-time()
decimal-date-time(${training_end_date}) - decimal-date-time(${training_start_date})

You cant get the entered value to appear as "40%" in the actual (integer) question itself, but you can certainly display the value the user entered in a subsequent note as a percentage:

type:integer, id:percent, label:"please enter percent"
type:note, label:"you entered ${percent}%"