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Forty-one's Forte (Posted on 2022-08-27) Difficulty: 3 of 5
Determine the quotient and remainder when 400....001 (100 zeros) is divided by 41.
Provide valid explanation for your answer.

See The Solution Submitted by K Sengupta    
Rating: 5.0000 (1 votes)

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Solution Solution without programming | Comment 2 of 5 |
Quotient: 9756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097561
Remainder:  0

Start with the remainder.
number of zeros; Number;  the Number mod 41:
0 zeros: 41      0
1 zero:  401     32
2 zeros: 4001    24
3 zeros: 40001   26
4 zeros: 400001   5
5 zeros: 4000001   0
6 zeros: 40000001  32

There is a repeating pattern such that when the number of zeros is 100, the remainder is in fact zero.

The quotients make a series that starts:
1, 9, 97, 975, 9756, 97561, 975609, ...
Except for the first '1' corresponding to 0 zeros, the number of digits in the quotient equals the number of zeros in the "400..001 number".

Look at 4/41 as per https://www.mathsisfun.com/calculator-precision.html
0.097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097561

Now, erase the "0.0" and just look at the first 102 characters starting with the "9":
975609756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097

Characters 100, 101, and 102 are  "097".
The 100-th digit is 0 but the next digit suggests converting this to "1" due to rounding.  

So the quotient should be:
9756097560975609756097560975609756097560975609756097560975609756097560975609756097560975609756097561

And this is confirmed at the mathsisfun website when the quotient is multiplied by 41.

  Posted by Larry on 2022-08-27 09:37:05
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