I have a missing page in a downloaded book . Have a duplicate page instead. How do I get that page? Book came from iTunes bookstore to my iPad?

Try deleting the ibook from the bookshelf in your iBooks app (there should be an Edit button top right) and redownload it via the Purchased tab in the ibookstore in the app : re-downloading.

If it re-downloads in the same state then try the 'report a problem' link from your purchase history : log into your account on your computer's iTunes via Store > View My Account and you should then see a Purchase History section with a 'see all' link to the right of it ; click on that and you should see a list of your purchases ; find that book and use the 'Report a Problem' link and fill in details about the problem (iTunes support should reply within, I think, 24 to 48 hours).

Some people have had a problem with the 'report a problem' link (it's been taking people to this site on a browser instead of showing a form in iTunes) - if it does that to you then try contacting iTunes support via this page : http://www.apple.com/support/itunes/contact/- click on Contact iTunes Store Support on the right-hand side of the page.