Using your Head is Permitted

October 2008 riddle

This cute little riddle was brought to my attention only very recently, but it immediately became an instant favorite with me. I'll give credits for its origin on the answer page.

The riddle concerns the number . The question is this: what is this number's 48th digit after the decimal point?

To be sure, one can solve this riddle with any calculator that has enough precision digits, but the point here is to solve it using your head. Answers will only be accepted if they entail a derivation proving what the required digit is, without requirng any arithmetic that one cannot perform easily in one's head.

Readers who wish to really enjoy this one will do well to avoid any use of calculators in approaching the riddle.

List of solvers:

Bojan Bašić (1 October 11:45)
Xiaohui Bei (1 October 16:04)
Hongcheng Zhu (1 October 18:16)
Albert Stadler (1 October 18:21)
Dan Dima (2 October 00:20)
Li Wei (2 October 00:23)
Lu Sida (4 October 21:16)
Wolfgang Kais (5 October 09:44)
Mark Tilford (7 October 08:02)
MyongHun Jo (8 October 03:16)
Dharmadeep Muppalla (10 October 20:47)
Itsik Horovitz (17 October 05:12)
Dong LiQian (19 October 20:58)
Ross Millikan (21 October 05:13)
Yingjie Xu (26 October 13:22)
Alex Wagner (29 October 10:34)

Elegant solutions can be submitted to the puzzlemaster at Names of solvers will be posted on this page. Notify if you don't want your name to be mentioned.

The solution will be published at the end of the month.


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