I think you could calculate it all with a single query like this:
Code:
$query = "SELECT (MIN(price)+MAX(price))/2 as median FROM condo03 WHERE (full_add like '%$Text_Box_1%' OR full_add like '%$Text_Box_2%' OR full_add like '%$Text_Box_3%' OR full_add like '%$Text_Box_4%') AND (status = '$status') AND (size >= '$Text_Box_15' AND size <= '$Text_Box_16') GROUP BY 'date' ASC");