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You can't use Migration Assistant to transfer only one app.
Have you got iWork on a DVD or purchased at the Mac App Store? If not, you should know that is difficult to make it work just by copying them to another Mac because they require some files in system folders. If you have iWork on a DVD, just insert it in the new Mac and install it.
If you purchased it at the Mac App Store, open the Mac App Store on your other Mac, go to Purchases tab and download iWork apps for free