This is the first book of Math Contest Books Series. The book introduces a powerful problem solving technique - the mass points method. The book can be used by students preparing for math competitions such as Mathcounts, AMC 10/12/AIME. Second book of Math Contest Books Series: https://www.amazon.com/Balls-Boxes-Yongcheng-Chen/dp/1540390578 Third book of Math Contest Books Series: The Area Method https://www.amazon.com/dp/1540856410 Fourth book of Math Contest Books Series: Problem Solving Using Cauchy's Inequality https://www.amazon.com/dp/1541000285 Fifth book: the Completing Square Method: https://www.amazon.com/dp/1542426626 9th book: Problem Solving Using Auxiliary Lines https://www.amazon.com/dp/1975681754 10th book: https://www.amazon.com/Problem-Solving-Using-Vietas-Theorem/dp/1542800056 - from Amzon