A number line is the best picture for decimals. Whole numbers split into tenths, tenths split into hundredths — and every decimal has its own spot on the line.
Draw a line from 0 to 1. Split it into ten equal jumps. Each tick mark is a tenth.
0 — 0.1 — 0.2 — 0.3 — 0.4 — 0.5 — 0.6 — 0.7 — 0.8 — 0.9 — 1
To find 0.6, count six ticks from 0. To find 0.7, count seven.
Going the other way — somebody marks a point and you have to say what decimal it is — is exactly what the practice exercise asks.
The recipe:
If the marker sits 4 ticks past 0 on a 0..1 line, it's at 0.4.
The same idea extends past 1.
0 — — — 1 — — — 2 — — — 3 — — — 4
Each whole-number interval splits into ten tenths. So a point five ticks past 2 sits at 2.5 (two and a half).
Between 0.4 and 0.5 there are nine more ticks for hundredths: 0.41, 0.42, 0.43, …, 0.49. To draw them, you zoom in.
0.4 — 0.41 — 0.42 — 0.43 — 0.44 — 0.45 — 0.46 — 0.47 — 0.48 — 0.49 — 0.5
Every tenth is just another small number line with ten smaller jumps.
Each tenth on the line has a matching fraction:
| Decimal | Fraction |
| 0.1 | |
| 0.2 | |
| 0.5 | |
| 0.7 | |
| 0.75 |
The number line lets you see why — both are about splitting a whole into equal parts.