What is Decimal writing? — Mathematics

Definition 25.3 Primary & Middle School Mathematics · Chapter 25 — Tenths and Hundredths

The number $2 + \frac{3}{10} + \frac{7}{100}$ is written

2.37

— the decimal point separates the whole part ( $2$ ) from the decimal part; the first digit after the point counts the tenths, the second the hundredths. Reading: “two point three seven”, or “two and thirty-seven hundredths”.

Zooming between 2 and 2.8: big marks every tenth, small marks every hundredth. The number 2.37 sits between 2.3 and 2.4, at the 7th small mark. — Zooming between $2$ and $2.8$ : big marks every tenth, small marks every hundredth. The number $2.37$ sits between $2.3$ and $2.4$ , at the $7$ th small mark.

Examples

Example 25.4

\frac{7}{10} = 0.7, \qquad \frac{43}{100} = 0.43, \qquad \frac{5}{100} = 0.05, \qquad 3 + \frac{4}{10} = 3.4 .

Careful with $\frac{5}{100}$ : five hundredths need a $0$ in the tenths place — $0.05$ , not $0.5$ .

Example 25.5 (Money is hundredths)

One cent is one hundredth of one euro (or dollar, or pound): a price of $4.85$ means $4$ whole coins and $85$ hundredths. Money is the decimal point you already use every day: $10$ cents $= 0.10$ ; two euros fifty $= 2.50$ ; and $0.05$ is a five-cent coin, not fifty!

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