Explaining Missing Decimal Numbers 3, 6 & 9 in Calculations

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Discussion Overview

The discussion centers around the observation of missing decimal numbers, specifically 3, 6, and 9, in the decimal expansions resulting from certain calculations involving fractions like 1/7. Participants explore the implications of these missing numbers in the context of long division and decimal representation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant presents calculations showing the decimal expansions of fractions such as 1/56 and 1/7, questioning the absence of certain digits in the results.
  • Another participant suggests that the missing digits are simply a result of the calculations, using the example of 1/3 to illustrate that not all digits are needed in decimal expansions.
  • A later reply acknowledges a mistake in the initial observation but emphasizes the interesting nature of the repeating decimal cycles, particularly with 142857.
  • Another participant elaborates on the long division process, explaining that the limited set of possible remainders (1 through 6) during division by 7 accounts for the absence of the digit 3 in the decimal expansion.
  • This participant further explains that the long division steps show that obtaining a remainder that would yield a 3 is not possible, as it would require a non-zero last digit that cannot occur in this context.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the missing digits, with some seeing it as a straightforward result of calculations while others find it an interesting phenomenon worthy of deeper exploration. No consensus is reached regarding the implications of these observations.

Contextual Notes

The discussion highlights limitations in understanding the long division process and the specific conditions under which certain digits appear or do not appear in decimal expansions. There is an acknowledgment of the complexity involved in these calculations without resolving the underlying mathematical steps.

Hippasos
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1/56=0,017857142857142857142857...142857

1/7=0,142857142857142857142857...142857

142857

142857/7=
20408,142857142857142857...142857

20408/7=
2915,42857142857142857...142857

2915/7=
416,42857142857142857142857...142857

416/7=
59,42857142857142857142857...142857

59/7=
8,42857142857142857142857...142857

8/7
1,142857142857142857142857...142857

Missing decimal numbers 3 - why are these"missing"? Not needed even during calculations - at all?

Can You please explain?
 
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what's to explain? it's just the result of particular calculations.

Hey, try 1/3 = .333333 you don't need 1,2,4,5,6,7,8, or 9 Explain that !
 
phinds said:
what's to explain? it's just the result of particular calculations.

Hey, try 1/3 = .333333 you don't need 1,2,4,5,6,7,8, or 9 Explain that !

Yes of course my stupid mistake. I was *runk and it was late. Still interesting ...142857.. cycles there.
 
Hey! don't dismiss your observation so quickly. It is very interesting and if you look at the long division process you can see just why there are no 3 or multiples of, in the decimal expansion.

First of all observe that there are at most 6 digits possible. There is a limited set of possible remainders in the long division process{1,2,3,4,5,6}. A zero would terminate the process, 7 and greater means that you have not made a correct choice of a multiplier. This implies that there can be at most 6 digits in the expansion. 7 is unique in that it is the only integer with the max possible number of unique digits in the decimal expansion.

Now let's go through the long division process and see if we can see why 3 does not appear.

The first step:

10/7 = 1 r 3 : so 1 is the first digit the remainder sets up the second step, r*10
30/7 = 4 t 2 : so 4 is the 2nd digit.
20/7= 2 r 6 : so 2 is the 3rd digit.

now we can see why 3 does not appear, each of the steps involves a multiple of 10 divided by 7. But the only way to get a 3 would be if you could have a non zero as the last digit, this cannot happen. Since 7*3=21 and 7*4=28.

I also find this an interesting little tidbit. Hope I helped throw some light on it for you.
 

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