If command doesnt work

there might be something wrong with my code below:

 $tal1 and $tal2 are randomised.

if ($_POST['matte'] != $tal1 + $tal2){
$ok = false;
$message6 = 'You must be able to count...!<br />';
}

somehow when I enter the correct amount the variable $ok is still false? If someone can help me I would really appreciate it.