Hokkaido University Science Mathematics 15 Years, 6th Edition Price: 2530 yen (tax included) Past questions from 2004 to 2018. I used this book because it's famous for having many high-quality problems, not just for those taking the Hokkaido University entrance exam, but also for anyone studying mathematics. I've underlined a few important parts, but it doesn't affect solving the problems at all. #Riichi Suehiro #Riichi_Suehiro #Book #Nature/Mathematics