Displaying Grouped File Info In Osx

I often want to check the size of a subset of folders on OS X. To do this I use finder:

The shortcut for viewing info in Finder is ⌘+I. This is great for single files. But what happens if you want a group of folders (or files)?

Result of ⌘+I

To get the summary of a group try the following.
Result of ⌘+⌥+I