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Y.5 Find missing numbers in decimal sequences

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What are decimal sequences?

A decimal sequence is a list of numbers that follow a specific pattern and include decimals. Each number in the sequence increases or decreases by the same amount, called the step or interval.

Example:
  • 0.5, 1.0, 1.5, 2.0, 2.5, …
Note

The difference between numbers in a decimal sequence can be a whole number or a decimal. Always check how much the numbers change from one term to the next.

How to find the pattern

To find a missing number in a decimal sequence, you must first identify the pattern or rule the numbers follow. You can do this by finding the difference between two numbers that are next to each other.

Steps:
  • Look at two numbers that are next to each other.
  • Subtract the smaller number from the larger one to find the interval.
  • Use that same interval to find the missing number(s).

Example: 2.4, 2.6, ____, 3.0

The difference between 2.4 and 2.6 is 0.2. Add 0.2 again to find the missing number: 2.8.

Note

You can use addition for increasing sequences and subtraction for decreasing sequences.

Using place value to help

Decimals follow the same place value rules as whole numbers. Each place to the right of the decimal point is ten times smaller than the one before it.

Example:
  • 0.1 means one tenth
  • 0.01 means one hundredth
  • 0.001 means one thousandth

Example: When the pattern adds 0.05 each time, you are increasing by five hundredths.

Note

Understanding place value helps you add or subtract decimals correctly when finding patterns.

Practice finding missing numbers

Once you know the pattern, use it to fill in missing terms in a sequence. Always double-check by continuing the pattern before and after the missing number.

Examples:
  • 4.2, 4.4, ____, 4.8 → Add 0.2 each time → Missing number: 4.6
  • 7.0, ____, 6.6, 6.4 → Subtract 0.2 each time → Missing number: 6.8
  • 1.25, 1.50, 1.75, ____ → Add 0.25 each time → Missing number: 2.00
Note

Writing down the rule for your pattern helps you stay consistent when solving longer sequences.

Real-world connections

Decimal sequences appear in many real-world situations, such as measuring weight, temperature, or money. Understanding patterns helps you estimate, compare, and predict values accurately.

Example:
  • A thermometer shows 98.2°F, 98.4°F, ____, 98.8°F → Each step increases by 0.2°F → Missing number: 98.6°F
Note

When working with decimals in real life, round carefully and check that your answers make sense for the situation.