This is the Hiden no Sansu (Secret Math) series from Tokyo Shuppan. A fun math problem set, a set of 3 books. - Set Contents: Hiden no Sansu Series 3 books (Final Edition, Introductory Edition, Advanced Edition) - Target Grade Level: 6th grade, for 4th and 5th graders - Features: A fun math problem set I bought these and never used them. The order card is still inside. There are no markings, and they appear to be in good condition. These have been stored for a long time, so I will sell them to someone who doesn't mind that. #HidenNoSansu #JuniorHighSchoolEntranceExam #Math #TokyoShuppan #Keimeisha Thank you for looking.