<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml " layout="vertical" creationComplete="init()">
    <mx:Script>
        <![CDATA[
            import mx.collections.ArrayCollection;
            [Bindable] private var marksCollection:ArrayCollection = new ArrayCollection();
           
            private function init():void{
                marksCollection.addItem({"Maths":84,"Science":90,"English":75});
                marksCollection.addItem({"Maths":82,"Science":89,"English":71});
                marksCollection.addItem({"Maths":78,"Science":80,"English":65});
                marksCollection.addItem({"Maths":65,"Science":60,"English":52});
                marksCollection.addItem({"Maths":98,"Science":99,"English":91});
                marksCollection.addItem({"Maths":90,"Science":92,"English":87});
            }
           
            private function calc():void{
                for each (var item:Object in marksCollection){
                    var total:Number = item.Maths + item.Science + item.English;
                    var perc:Number = Math.round((total/300)*100);
                    item.Total = total;
                    item.Percentage = perc + "%";
                }
                marksCollection.refresh();
            }
        ]]>
    </mx:Script>
    <mx:Button label="Calculate" click="calc()"/>
    <mx:DataGrid width="100%" height="100%" dataProvider="{marksCollection}">
        <mx:columns>
            <mx:DataGridColumn dataField="Maths" headerText="Maths"/>
            <mx:DataGridColumn dataField="Science" headerText="Science"/>
            <mx:DataGridColumn dataField="English" headerText="English"/>
            <mx:DataGridColumn dataField="Total" headerText="Total"/>
            <mx:DataGridColumn dataField="Percentage" headerText="Percentage"/>
        </mx:columns>
    </mx:DataGrid>
       
</mx:Application>