-- No tens plus 49 ones.
-- One ten plus 39 ones.
-- Two tens plus 29 ones.
-- Three tens plus 49 ones/
==> Four tens plus 9 ones.
-- Five tens minus a single one.
-- Six tens minus 11 ones.
-- Seven tens minus 21 ones.
-- Eight tens minus 31 ones.
.
.
etc.
The heavy one is the way we actually write it.
That's what the digits '4' and '9' mean.
