<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$("#txtQuantity").blur(function(){
var price = $("#lblPrice").text();
var totalAmount = $("#lblTotal");
var toal = parseFloat(this.value) * parseFloat(price);
totalAmount.text(total);
});
});
</script>
Quantity: <asp:TextBox id="txtQuantity" runat="server" />
<br />
Price: <asp:Label id="lblPrice" runat="server" Text="10" />
<br />
Total Amount: <asp:Label id="lblTotal" runat="server" />
<br />