perplexus.info :: Just Math : Lucky seven III

Lucky seven III (Posted on 2011-01-05)

N is a base ten positive integer formed by writing the digit 7 precisely 2010 times, that is N = 77....77 (2010 times).

Determine the digital root of [N/199].

Note: [x] denotes the greatest integer ≤ x.

*** For an extra challenge, solve this problem without using a computer program.

Submitted by K Sengupta

Rating: 4.6667 (3 votes)

Solution: (Hide)

The required digital root is equal to 6.
For an explanation, refer to the analytical solution submitted by Brian Smith in this location.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
Puzzle Thoughts	K Sengupta	2024-02-15 21:33:04
Fookkat Network	fookkat	2024-02-15 19:54:49
Analytic Answer	Brian Smith	2016-07-04 11:56:23
A lot of 7's	Math Man	2011-01-05 15:28:21
With only a little cheating	Jer	2011-01-05 14:58:35
without the extra challenge (spoiler)	Charlie	2011-01-05 14:42:16

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