0.1234567945849: Round off the mixed repeating (recurring) decimal number to the nearest billiardth (12 decimal places)

Rounding a number means replacing it with a simpler, shorter approximation, while keeping its value close to the initial one. The rounded number will be less accurate, but easier to work with.

A repeating decimal has a number of decimals that repeat over and over again, infinitely: 0.1234567945849 ≈ 0.123456794584967945849...

Our number is sitting on the axis of numbers between two 12 decimal place consecutive neighboring numbers:
0.123456794584 < 0.1234567945849 < 0.123456794585

Our number is to be rounded off to one of these neighbors, the closer one.

The middle of this interval, the number that is equally close to the either neighbor, is: (0.123456794584 + 0.123456794585) ÷ 2 = 0.1234567945845

Our number, 0.1234567945849 ≈ 0.123456794584967945849..., is larger than 0.1234567945845, so it is closer to the larger neighbor: 0.123456794585

Except for 'To Ceiling, To Floor', the rounded off number (both the positive and the negative) will be equal only to this larger neighbor.

Rounding digit. Let's call the digit of the position place that is intended to round off to as the 'rounding digit'. The digit is 4: 0.123456794584967945849...

In a positive number, if the digit to the right of the 'rounding digit' is larger than 5, then the number is rounded to the larger neighbor.

The digit is 9: 0.123456794584967945849... ≈ 0.123456794585 rounded to the nearest billiardth (12 decimal places).

Or, even simpler.
In any number rounded to decimal places, if the digit to the right of the 'rounding digit' is 5 (but it is not the last non-zero digit to the right) or more than 5, ie. 6, 7, 8 or 9, then increase the 'rounding digit' by 1 and drop all the digits to the right of it, 4 + 1 = 5:

0.123456794584967945849... ≈ 0.123456794585 rounded to the nearest billiardth (12 decimal places)

Half Up, Half Down, Half Away From Zero, Half Towards Zero, Half to Even, Half to Odd. To Ceiling, To Floor.

Number Round Half Up:

Numbers that are halfway between two neighbors are rounded off to the larger neighbor. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Half Down:

Numbers that are halfway between two neighbors are rounded off to the smaller neighbor. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Half Away From Zero:

Numbers that are halfway between two neighbors are rounded off to the neighbor which is farther away from zero. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Half Towards Zero:

Numbers that are halfway between two neighbors are rounded off to the neighbor which is closer towards zero. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Half to Even:
(Gaussian Rounding or Banker's Rounding)

Numbers that are halfway between two neighbors are rounded off to the neighbor with an even rounding digit. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Half to Odd:
(Gaussian Rounding or Banker's Rounding)

Numbers that are halfway between two neighbors are rounded off to the neighbor with an odd rounding digit. 0.1234567945849 is not halfway between its neighbors.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)

Number Round Ceiling:

All the numbers that are between two neighbors are always rounded off to the larger neighbor.

0.1234567945849 ≈ 0.123456794585

- 0.1234567945849 ≈ - 0.123456794584

rounded to the nearest billiardth (12 decimal places)

Number Round Floor:

All the numbers that are between two neighbors are always rounded off to the smaller neighbor.

0.1234567945849 ≈ 0.123456794584

- 0.1234567945849 ≈ - 0.123456794585

rounded to the nearest billiardth (12 decimal places)