how to bind width of child element to width of parent element in silverlight

Question

I have a grid whose width is \"1*\". So the actual width decided at runtime I think. Within that grid I have another grid whose width I want to set to the runtime width of paren

Answer 1

 Width="{Binding Width, RelativeSource={RelativeSource AncestorType={x:Type Parent}, Mode=FindAncestor}}"

if both controls DataContext is different.