Ajax Toolkit Slider... can I use javascript to modify a second textbox based on slider value?

OK, I want to use the slider control to control a value that goes into a db... In this case, think of an estimate for a project, and we want to use the slider to modify the proportion of time for two different activities. So, if you keep the slider in the middle, 50% of the time will go to each activity. If you want to give "design" more time, slide toward the design end; if more project management, slide the other way.

So, I know the slider control will effect change to the Bound Control, but I want a second control that would be the value of the BoundControl subtracted from 100 (to give the alternate percentage).

<ajaxToolkit:SliderExtender ID="SliderExtender" runat="server"
        Minimum="0"
    Maximum="100"
    TargetControlID="PercentageSlider"
    BoundControlID="ManagementPercentage"
    Orientation="Horizontal"
    EnableHandleAnimation="true" /><asp:TextBox ID="PercentageSlider" runat="server"></asp:TextBox> <br /><asp:TextBox ID="ManagementPercentage" runat="server"></asp:TextBox><br /><asp:TextBox ID="DesignPercentage" runat="server"></asp:TextBox>

So, is it possible to use a javascript control to make the "DesignPercentage" textbox display a value that's (100 minus ManagementPercentage )?