If January 1st is a Wednesday, what day of the week is October 10th? Can You Solve It?

Gakken Inc. (Shinagawa-ku, Tokyo / President and CEO: Tatsuya Minami), a group company of GAKKEN HOLDINGS CO., LTD. (Shinagawa-ku, Tokyo / President and CEO: Hiroaki Miyahara), has started pre-orders on July 16, 2026, for the book titled 'If January 1st is a Wednesday, What Day is October 10th? The Book That Lets You Solve It in 10 Seconds' (scheduled for release on August 27, 2026).

'If January 1st is a Wednesday, what day of the week is October 10th?'

Out of the blue—can you solve this problem?

This is a type of question known as 'calendar calculation' (nichirekizan), commonly seen in middle school entrance exams.

You might find yourself wondering, 'What day would that be?' and feel the urge to solve it.

However, this problem—finding the day of the week without looking at a calendar—is notoriously difficult, with many students saying things like, 'I always make a calculation mistake' or 'My answer is always off by one day.'

It's such a tough problem that it has even appeared in entrance exams for prestigious schools like Oin Junior High and Kaisei Junior High.

But with a secret solving method, even this kind of problem can be solved 'by anyone,' 'easily,' and 'in seconds'!

The book 'If January 1st is a Wednesday, What Day is October 10th? The Book That Lets You Solve It in 10 Seconds,' which reveals this method, will be released on Thursday, August 27, 2026, and pre-orders are now open.

The name of this method? The 'Kuinihage Method'—a technique you won't find through any online search!

The author of this book is Toru Tanabe, known for the 'Time-Killer Drill' series, which has surpassed 500,000 copies in total print run.

As head of Ringo Juku, he is a math education specialist who has produced gold medalists in the Math Olympiad for nine consecutive years.

In this book, Mr. Tanabe reveals for the first time his original solving method, the 'Kuinihage Method,' developed through years of teaching experience.

Because it's an original method, searching for 'Kuinihage Method' online yields no results!

The exact technique remains a surprise until you read the book.

Though the name 'Kuinihage Method' sounds a bit alarming, the actual method is surprisingly simple and fun—something that will make you go, 'Wait, is it really this easy?'

*As of July 16, 2026, according to Gakken's research.

Target audience: Anyone aged 10 to 120 who enjoys intellectual games!

While this book focuses on calendar calculation problems seen in middle school entrance exams, it's not just for students.

The target readers are 'people aged 10 to 120 who enjoy intellectual play.'

After reading this book, you'll be able to figure out from today's date and day of the week 'what day of the week my birthday falls on this year' or 'on what day of the week my father was born.'

When you show this to family or friends, they'll be amazed like watching a magic trick—'Whoa, how did you do that?'—and the conversation will instantly liven up.

If January 1st is a Wednesday, what day is October 10th?

Once you know the 'Kuinihage Method,' you'll be able to solve it in just 10 seconds.

If you want to discover this secret, be sure to read this book.

[Product Overview]

'If January 1st is a Wednesday, What Day is October 10th? The Book That Lets You Solve It in 10 Seconds'

Author: Toru Tanabe

Price: 1,320 JPY (tax included)

Scheduled Release Date: August 27, 2026

Specifications: B6 modified size, 96 pages

E-book version: Available

ISBN: 978-4-05-306405-9

[Book Details and Pre-order Links]

・Gakken Publishing Site: https://hon.gakken.jp/book/1130640500

・Amazon: https://www.amazon.co.jp/dp/4053064058

・Rakuten Books: https://books.rakuten.co.jp/rb/18661517/

<E-book>

・Kindle: https://www.amazon.co.jp/dp/B0H4Q3KT5C

・Rakuten Kobo: https://books.rakuten.co.jp/rk/2004fdf3c2083a13b8776a15a793318f

Gakken Inc.

https://www.corp-gakken.co.jp/ ・President and CEO: Tatsuya Minami ・Incorporation Date: January 13, 2009 (Company name changed on October 1, 2022) ・Capital: 50 million JPY ・Head Office: 2-11-8 Nishigotanda, Shinagawa-ku, Tokyo 141-8416 ・Business: Publishing and content, global operations, medical and nursing publishing, products for kindergartens and schools, classroom-related services, e-commerce and online services, advertising

GAKKEN HOLDINGS CO., LTD.

https://www.gakken.co.jp/ ・President and CEO: Hiroaki Miyahara ・Incorporation Date: March 31, 1947 ・Capital: 19,817 million JPY ・Sales: 199.1 billion JPY, 82 consolidated subsidiaries (as of fiscal year ending September 2025) ・Listed on the Tokyo Stock Exchange Prime Market (Stock Code: 9470) ・Head Office: 2-11-8 Nishigotanda, Shinagawa-ku, Tokyo 141-8510 ・Phone: 03-6431-1001 (main) ・Business: Holding company established in 1946, operating in education and healthcare/welfare Education: Classroom and tutoring services including 'Gakken Juku,' publishing and content such as learning materials, kindergarten and school supplies including textbooks Healthcare/Welfare: Service-oriented housing for the elderly, dementia group homes, childcare and after-school support Global: Operations in over 150 countries