There are two bookshelves, A and B. Shelf A has $$1100$$ books, and shelf B has books $$300$$. We need to take  books from shelf A to shelf B, so that books in shelf B is three times more than self A. 
Overseas Competition->Knowledge Point->Word Problem Modules->Questions Involving Sum, Difference and Multiples->Problems Involving Sum and Difference->Problems Involving Sum and Difference with Two Variables
The sum is unchanged, which is $$1400$$，$$1400\div \left( 3+1 \right)=350$$，$$1100-350=750$$． 