Annie had twice as many paper clips as Beth, After Beth had used $$15$$ paper clips, Annie had $$4$$ times as many as Beth. How many paper clips did Annie have? 
Overseas Competition->Knowledge Point->Word Problem Modules->Questions Involving Sum, Difference and Multiples->Questions Involving Varying Multiples
Let the number of Annie\textquotesingle s and Beth\textquotesingle s be 2n and n. 2n=4(n-15), so n=30, 2n=30 