Decimal numbers are used to represent parts of a whole.
A decimal point ( . ) separates the whole number part from the fractional part.

For example, in the number 325.678:

  • 325 is the whole number part
  • 678 is the fractional part

Each digit in a decimal has a place value:

PlaceExample_DigitValue
Hundreds3300
Tens220
Units55
Tenths60.6
Hundredths70.07
Thousandths80.008

Therefore:

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Terminating Decimal Numbers

A terminating decimal is a number that has a finite number of digits after the decimal point.
It comes to an end — it doesn’t go on forever.

Examples:

All of these stop after a certain number of digits.

Worked Example

Convert the fraction seven-eighths into a decimal.

We divide 7 by 8:

The decimal ends after three places, so it is terminating.

Non-Terminating Decimal Numbers

A non-terminating decimal goes on forever — it has an infinite number of digits after the decimal point.

These are of two types:

  • Recurring (Repeating)
  • Non-Recurring (Non-Repeating)

a) Recurring Decimal Numbers

A recurring decimal has a set of digits that repeat indefinitely in a fixed pattern.

Examples:


The bar (overline) indicates the repeating digits.

Worked Example 1 — Pure Recurring Decimal

Convert into a fraction.

Let:

Multiply both sides by 10:


Subtract the first equation from this:

Worked Example 2 — Mixed Recurring Decimal

Convert into a fraction.

Let:

Multiply by 1000 (to move the decimal just before the repeating part):

Multiply by 10 (for one repeat shift):

Subtract:

b) Non-Recurring Decimal Numbers

These are non-terminating decimals that do not repeat.
The digits after the decimal point go on forever without any pattern.

Such numbers are called irrational numbers.

Examples:


They neither stop nor repeat.

Worked Example

Show that is a non-terminating, non-recurring decimal.

Using a calculator:

The digits go on infinitely and show no repeating pattern.

Therefore, is non-terminating and non-recurring, and hence irrational.

Rounding Decimal Numbers

Sometimes, we need to round decimals to a specific place value (e.g., 1 decimal place, 2 decimal places).

Rule:

  1. Identify the digit in the place value you’re rounding to.
  2. Look at the next digit (to the right): If it’s 5 or more, round up; if it’s less than 5, leave it.

Worked Example

Round 567.81456 to 3 decimal places:

The value in the 3rd decimal place position is 4. The next digit is 5, so we round up, taking the previous digit from 4 → 5.

Final answer: 567.815

Summary

Decimal numbers express whole and fractional parts using a decimal point. They can be terminating, recurring, or non-recurring. Terminating and recurring decimals are rational, while non-recurring decimals are irrational. Recognising these types helps in understanding number patterns, rounding, and fraction conversions.

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Gianpiero Placidi

UK-based Chemistry graduate with a passion for education, providing clear explanations and thoughtful guidance to inspire student success.