251.5: Round off the pure repeating (recurring) decimal number to the nearest hundredth (2 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: 251.5 ≈ 251.555555555555555...

Our number is sitting on the axis of numbers between two 2 decimal place consecutive neighboring numbers:
251.55 < 251.5 < 251.56

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: (251.55 + 251.56) ÷ 2 = 251.555

Our number, 251.5 ≈ 251.555555555555555..., is larger than 251.555, so it is closer to the larger neighbor: 251.56

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 5: 251.555555555555555...

In a positive number, if the digit to the right of the 'rounding digit' is equal to 5 and it is not the last digit that is different from zero, then the number is rounded to the larger neighbor.

The digit is 5: 251.555555555555555... ≈ 251.56 rounded to the nearest hundredth (2 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, 5 + 1 = 6:

251.555555555555555... ≈ 251.56 rounded to the nearest hundredth (2 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. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 decimal places)

Number Round Half Down:

Numbers that are halfway between two neighbors are rounded off to the smaller neighbor. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 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. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 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. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 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. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 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. 251.5 is not halfway between its neighbors.

251.5 ≈ 251.56

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 decimal places)

Number Round Ceiling:

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

251.5 ≈ 251.56

- 251.5 ≈ - 251.55

rounded to the nearest hundredth (2 decimal places)

Number Round Floor:

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

251.5 ≈ 251.55

- 251.5 ≈ - 251.56

rounded to the nearest hundredth (2 decimal places)