there are 2 opinions on the amount of lashes one says 39 and one says 40:
when would they agree to give the same amount?
when the guy being lashed had done 40 aveirot which deserve lashes.the 40th is that he gave someone 40 lashes.
so the opinion which says you do 39 its 39 times 40(the fortieth being for adding a lash)
the opinionwhich says 40 does not count the 40th aveirot so its 40 times 39.
Oy now is that not gevaldik?