Decimal place value
Place value counts ones, tens and hundreds. What do the digits to the right of a decimal point count?
Where you are 4 inside
What this area is about
Cut one whole into ten equal parts and each part is a tenth; cut a tenth into ten and each part is a hundredth, and so on. The digits after the decimal point count these pieces. Each place is worth one tenth of the place to its left, the same rule whole numbers already follow, carried past the point.
How these fit together
The places. Tenths and hundredths defines the first two places, \displaystyle 0.1 = \frac{1}{10} and \displaystyle 0.01 = \frac{1}{100}. Thousandths adds the third, \displaystyle 0.001 = \frac{1}{1000}, and writes decimals in standard, expanded and word form.
Using the places. Decimals on a number line places a decimal by cutting the gap between two whole numbers into ten equal parts. Comparing and ordering decimals lines up the decimal points and compares place by place from the left.
A path through it
Tenths and hundredths come first. Thousandths, the number line and comparing follow, in any order.
Finish here and you are ready for decimal arithmetic, rounding decimals, money written as decimals and, later, scientific notation.