I have purchased Manhattan SC guide and have an online account. Please let me know from where can I get "250+ challenge math questions". I guess I am eligible for that set as I am already using a Manhattan product.
The challenge problem archive is a separate product from the books, which include CAT exam access and a question bank that has questions of varying difficulty on the topics included in each book. To get access to the challenge problem archive, you can visit our online store: http://www.manhattangmat.com/Store.cfm