PHP - Am I Just Bad At Math, Or Is My Calculator Wrong?

Website: http://novacms.vacau.com/index.php

I'm trying to make a calculator for this game I play, it's fully developed, but with one bug. It doesn't do the math right.

$goal = The amount of EXP (Experience Points) someone wants to get
$exp = The amount of EXP they currently have
$npcs_exp["exp"] = The amount of EXP the monster has

But, when they enter in the information, the calculation is all screwed up. When I do it, it seems to give me the same number EACH time.

The part where the calculation "goes down". Remember, I'm trying to see how many times you need to kill a NPC to achieve your goal.


//math
$npc_exp_extract = mysql_query("SELECT exp FROM npcs WHERE name='$npc'");
$npcs_exp = mysql_fetch_assoc($npc_exp_extract);

$amount = $goal / $npcs_exp["exp"];


Full code:


<?php
$exp = $_POST["exp"];
$npc = $_POST["npc"];
$goal = $_POST["goal"];

mysql_connect("removed", "removed", "removed");
mysql_select_db("a2248602_npcs");

if(!$goal || !$npc || !$exp)
{
echo "<center><form action='index.php' method='POST'>GOAL: <input type='text' name='goal'> Current XP: <input type='text' name='exp'>";
echo "NPC: <select name='npc'>";

$npc_extract = mysql_query("SELECT * FROM npcs");
while($npcs = mysql_fetch_assoc($npc_extract))
{
 echo "<option name='". $npcs['name'] ."'>". $npcs['name'] ."</option>";
}

echo "</select> <input type='submit'></form></center>";
}
else
{
//math
$npc_exp_extract = mysql_query("SELECT exp FROM npcs WHERE name='$npc'");
$npcs_exp = mysql_fetch_assoc($npc_exp_extract);

$amount = $goal / $npcs_exp["exp"];

if($amount=="1")
{
echo "You will need to kill a <b/>". $npc ."</b> <b>". $amount ."</b> more time. You earn ". $npcs_exp["exp"] ." XP for each kill from this NPC. | <a href='index.php'>Do another</a><br/><br/>";
}
else
{
echo "You will need to kill a <b/>". $npc ."</b> <b>". $amount ."</b> more times. You earn ". $npcs_exp["exp"] ." XP for each kill from this NPC. | <a href='index.php'>Do another</a><br/><br/>";
}
}

echo "<center>Made by Zaros from <a href='creation-x.net'>Creation-X</a></center>";
?>


Mod edit: DB credentials removed.