Correct math and limerick.

Seen in FreeBSD just recently:
http://svnweb.freebsd.org/base?view=revision&revision=268295
And NetBSD 14 years ago:
http://cvsweb.netbsd.org/bsdweb.cgi/src/games/fortune/datfiles/fortunes2.diff?r1=1.6&r2=1.7&only_with_tag=MAIN