Foundational math vocabulary
Decimal
Pronunciation: DESS-uh-mul
A decimal writes a number using place values to the right of a decimal point.
0.10.01Foundational
Plain language
What it means
A decimal writes a number using place values to the right of a decimal point.
Formal meaning
Mathematical definition
A finite decimal is a base-ten positional representation containing tenths, hundredths, thousandths, and further negative powers of ten.
Where it fits
Its place in mathematics
Decimals provide a compact way to write fractions, measurements, money, data, and scientific values.
Why it matters
The practical reason to learn it
They make place-value comparison and many calculations easier to record.
Worked example
Convert a fraction
Write 3/4 as a decimal.
- Divide 3 by 4 or create an equivalent fraction with denominator 100.
- 3/4 = 75/100.
3/4 = 0.75.
Real-life example
Where this appears
A machinist reads decimal measurements to control the size of a manufactured part.
Common mistake
What to watch for
Thinking 0.8 is smaller than 0.75 because 8 is smaller than 75. Compare equal place values: 0.80 and 0.75.
Memory tip
Keep this in mind
Add trailing zeros when comparing decimals; they do not change the value.
Little-known fact
Keep curiosity alive
Some fractions produce decimals that repeat forever rather than terminate.
A profession that uses this idea
Tolerances are written in decimals
Design and manufacturing drawings use decimal dimensions and tolerances to communicate precision.
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Prerequisites, related ideas and next concepts
People behind the ideas
Related Math Heroes
Simon Stevin
Simon Stevin was engineer, mathematician, and military adviser. He promoted decimal fractions and wrote on statics, hydrostatics, bookkeeping, and navigation.
Jamshid al-Kashi
Jamshid al-Kashi was mathematician and astronomer. He calculated pi to many sexagesimal places, worked with decimal fractions, and produced highly accurate trigonometric values.
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