A chunk of pages is missing from a book. The sum of the missing page numbers is 9808. What are those page numbers?
The pages numbered 291 through 322 are this missing pages.
As the sum of page numbers from 1 to n is a triangular number [that is, equal to n(n+1)/2], the sum of page numbers of the chunk of missing pages can be formulated, where X is the final missing page and Y is the first missing page, as:
X(X+1)/2  Y(Y1)/2 = 9808.
322(323)/2  291(290)/2 = 9808

Posted by Dej Mar
on 20091113 17:37:58 