A learning book for elementary school students with plenty of mental calculation practice problems that can be solved in 5 seconds. - Title: The Book That Allows Elementary School Students to Mentally Calculate Up to 19x19 in Just One Day - Publisher: Gakken Plus - Target age: Elementary school students - Number of pages: 121 pages - Contents: Abundant practice problems to increase mental calculation speed - Features: Problems that can be solved in 5 seconds are included - Price: Regular price 1100 yen - Author: Takuya Kosugi Thank you for viewing. I bought it and read it a few times. There is a slight fold on the cover, but the inside is clean and there is no problem with reading it. Please refrain from purchasing if you are concerned about minor details, as it is stored by an amateur. Thank you very much.