Brain-Training is an innovative new series of six unique, colour illustrated puzzle books. They are designed to help you make the most of your brain power by solving puzzles that increase slowly in level of difficulty. The puzzles get progressively tougher over the six titles and the second batch comprises Quick Brain-Training 2, Medium Brain-Training 2 and Difficult Brain-Training 2. They pick up where Quick Brain-Training 1, Medium Brain-Training 1 and Difficult Brain-Training 1 left off. This allows you to plot your progress and see how well you are developing.Quick 1 and Quick 2 contain a high concentration of easier puzzle-types - still stimulating and very useful for development - like Spot-the-Difference, Missing Word, Silhouette, as well simpler versions of Sudoku, Kakuro and the like. By the time you reach the Difficult books 1 and 2 you'll be ready for the extremely tough challenges that await: Super-hard Sudoku, frustratingly tough Make a Pair and the word/logic puzzle hybrid Yudoku.Buy them one by one and progress slowly, or work your way the entire series as fast as you can - the pace is up to you, but one thing is for sure, you will notice an improvement in your puzzle-solving abilities.