Good point. Based on the problem description as given in the OP, it looks like there should be a range of values accepted between 9 and 10, as well as between 99 and 100.

(Oops... if the instructor who handed out the homework was expecting that little detail to turn it into a "trick question", I probably just gave away the surprise.)

Helpful hint for the truly ambitious student: get extra credit by making sure the regex covers e and π as well -- both of them are in the specified range. ;)