关于一个页面内的input即时计算的问题！

3个input,前两个是数据输入框一样，最后的input是前两个input数据相加的显示结果，
要求是前面的两个input的数据和动态输出到第三个input

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1<input id="i1" onpropertychange="c()"/>

1<input id="i2" onpropertychange="c()"/>

1<input id="i3"/>

1<script>   
2function c(){   
3with(document.all){   
4i3.value=Number(i1.value)+Number(i2.value)   
5}   
6}   
7</script>

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1<input id="t1" onpropertychange="t1change()"/>

1<input id="t2" onpropertychange="t2change()"/>

1<input id="t3"/>

1<script>   
2function t1change(){   
3if (!t2.value) t3.value=t1.value   
4}   
5  
6function t2change(){   
7t3.value=t1.value*1+t2.value*1   
8}   
9</script>

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1<form name="form1">
2<input name="txt1" ondragenter="return false" onkeypress="return event.keyCode&gt;=48&amp;&amp;event.keyCode&lt;=57 ¦ ¦event.keyCode==46" onpaste="return !clipboardData.getData('text').match(/\D/)" onpropertychange="jia()" style="ime-mode:Disabled"/><br/>
3<input name="txt2" ondragenter="return false" onkeypress="return event.keyCode&gt;=48&amp;&amp;event.keyCode&lt;=57 ¦ ¦event.keyCode==46" onpaste="return !clipboardData.getData('text').match(/\D/)" onpropertychange="jia()" style="ime-mode:Disabled"/><br/>
4<input name="txt3" readonly=""/>
5</form>

1<script language="javascript">   
2function jia()   
3{   
4var n1 = document.form1.txt1.value;   
5var n2 = document.form1.txt2.value;   
6document.form1.txt3.value = parseFloat(n1) + parseFloat(n2);   
7}   
8</script>