First, be sure to load the MathObjects.pl macros via
loadMacros("MathObjects.pl");at the top of your problem.
Second, if you don't want the correct answer to appear as $num-1 (e.g., if $num is 3, the correct answer will show as 3-1), then you can do either
$new = Compute($num-1);(with no quotation marks, so the subtraction is done first and THEN
Compute()is called on the result), or
$new = Real($num-1);which creates a Real MathObject directly.
Good luck with your authoring.
Davide PS, if you are using the reply form to enter your message, you can enter <code>...</code> directly, but if you are using the WYSIWYG editor, then you can't enter HTML directly (though you could probably select a monospace font). I have also been unhappy about no preview, but once you post you can continue to edit for 30 minutes, so that's almost like a preview.