Using variables in printf format

Question

Suppose I have a file like this:

$ cat a
hello this is a sentence
and this is another one

And I want to print the first two columns with so

Answer 1

does this count?

idea is building the "dynamic" fmt, used for printf.

kent$   awk '{n=7;fmt="%"n"-s%s\n"; printf fmt, $1, $2}' f 
hello  this
and    this