<script language="JavaScript" />
function Display_num() {
//대입 숫자
var num1=document.getElementById("num1").value;
var num2=document.getElementById("num2").value;
var num3=document.getElementById("num3").value;

//연산자
var operation1=document.getElementById("operation1").value;
var operation2=document.getElementById("operation2").value;
//결과값 넣기
document.getElementById("is_nums").innerHTML =eval(num1+operation1+num2+operation2+num3);


}
</script>


<input type="text" id="num1" style="width:70px;" value="" />
<select id="operation1" style="width:70px;">
<option value=''>연산</option>
<option value='*'>곱하기</option>
<option value='/'>나누기</option>
<option value='+'>더하기</option>
<option value='-'>빼기</option>
</select>
<input type="text" id="num2" style="width:70px;" value="" />
<select id="operation2" style="width:70px;">
<option value=''>연산</option>
<option value='*'>곱하기</option>
<option value='/'>나누기</option>
<option value='+'>더하기</option>
<option value='-'>빼기</option>
</select>
<input type="text" id="num3" style="width:70px;" value="" />



<div id="is_nums">계산 결과</div>
<a href="#" onclick="Display_num();return false;">계산하기</a>

JAVASCRIPT

<script>
var result = 2*10/5; //result는 변수명

document.write(result); // 화면에 출력
alert(result); // 경고창을 띄움
</script>





PHP

<?php
print (2*10/5); //print 대신 echo를 써도 상관 없음
?>


HTML은 불가합니다 ;)