I got a number of people who answered "<", but putting that symbol between the two numbers does not "result in a number that is greater than the first number but less than the second number", as the puzzle stipulated. 228<456 is simply a true statement.
Other answers included 1 and 3. But 2281456 and 2283456 are not between 228 and 456.
The correct answer is a decimal point, as a number of you correctly responded, with Mary being the first. 228.456 is greater than 228 and less than 456.
Thanks for playing!