ShowImg Function - Display Random Images

I have to access code in an external javascript page (random.js) which I have done. But then I have to create a second script element to create the function showlmg() and within that I require statements to declare a variable named imgNumber equal to the value returned by the randomInteger() (which is from the external sheet found in data files from the textbook therefore I know they are right). I am supposed to use 9 as the value of the size parameter in the randomInteger() function. The second statement should be command that writes the following text to the document: <img src='imgNumber.jog' alt= ' '/>.

So basically the coding I have done is:
<script type= "text/javascript" src= random.js"> </script>
<script type="text/javascript">
function showlmg() {
var imgNumber= randomInteger(9);// Return a random number from 0 to 9.
document.write("<img src='imgNumber.jpg' alt=''/>");
}
</script>

All in the head of the document and then
function randomInteger(size) {
return Math.floor((size+1)*Math.random());} from the external file.
and
<tr>
<td colspan="2" class="center">
<script type= "text/javascript">
showlmg();
showlmg();
showlmg();
showlmg();
showlmg();
</script>
</td>
</tr>

To post in a table on the page... I believe the issue is in the declaring a variable the is equal to the result of the function random integer which the text book or anywhere that I can find online fails to explain how to do.