As a matter of a fact - your code will give you absolutely NOTHING!
Let me first explain you few things,
-now that you've learned that Java and JavaScript are two completely different languages, there is no single line in your code where you didn't put at least one [?deliberate!] error.
vars can be declared either separately:
var one;
var two;
var three;
or grouped with one keyword in a comma-separated list:
This will produce another error:
there is no comma between "tw" & "o", or there is an illegal whitespace in the name of var.
(your number 1 error reproduced).
You've commented your script <!-- ... <-- , this can never happen to be one of a "new to Java" error.
You have deliberately missmathched quotes
window.prompt( 'Enter the first number", "0" ); in every single line required.
You've managed to switch "I" with "L" in every parselnt( firstNumber ); function counting on similar visual representation of I and smallcaps L in fonts currently used.
Finishing with your special mess:
window.status =( sum: " + sum + ");
using undefined sum: but converting the existing "sum" var into a string literal with no meaning at all.
Not to forget your prime error <script type="text/javajscript"> requiring the browser to use an unknown and inexistent scripting language to interpret your javascript. The most fundamental of all errors previously mentioned.
To round it up, your <body onload="window.prompt;"> is absolute nonesense.
That's because you didn't write anything of that kind in your (provided) code!
Ok this is what I have so far! You will agree its better that what I had when I first posted:
<script LANGUAGE="JAVASCRIPT">
var firstnumber = prompt("Enter first number and Click OK", "0");
var secondnumber = prompt("Enter second number and Click Ok", "0);
var thirdnumber = prompt("Enter third number and Click Ok", "0);
var total = Math.floor(firstnumber)+ Math.floor(secondnumber)+ Math.floor(thirdnumber);
alert("The Sum is: " + total ) // this line give me the correct sum! But I need average, product, smallest and largest of the numbers as well.
alert("The Sum is: " + total + " Average: " + average + " product: " + product +" largest " + largest + " smallest " + smallest) //when I try to replace the above line with this one I get errors.
function YourCost1(){
if(firstnumber > secondnumber && firstnumber > thirdnumber){
var largest= firstnumber;
}
else if(secondnumber > firstnumber && secondnumber > thirdnumber){
var largest= secondnumber;
}
else if(thirdnumber > firstnumber && thirdnumber > secondnumber){
var largest= thirdnumber;
}
if(firstnumber < secondnumber && firstnumber < thirdnumber){
var smallest= firstnumber;
}
else if(secondnumber < firstnumber && secondnumber < thirdnumber){
var smallest= secondnumber;
}
else if(thirdnumber < firstnumber && thirdnumber < secondnumber){
var smallest= thirdnumber;
}
}
</SCRIPT>
Unsolved 
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