What is Classes? — Mathematics

Definition 21.1 Primary & Middle School Mathematics · Chapter 21 — Large Numbers

Starting from the right, the digits of a number are grouped in classes of three: the class of units, the class of thousands, the class of millions. Each class has its own units, tens and hundreds. For instance

6\,309\,452 = 6 \text{ millions} + 309 \text{ thousands} + 452 \text{ units},

read “six million three hundred nine thousand four hundred fifty-two”.

The class table of 6\,309\,452 (h = hundreds, t = tens, u = units of each class). Reading a large number means reading each class, followed by its name. — The class table of $6\,309\,452$ (h $=$ hundreds, t $=$ tens, u $=$ units of each class). Reading a large number means reading each class, followed by its name.

Examples

Example 21.2 (Writing with the classes)

“Twelve million forty thousand five hundred” has $12$ in the millions class, $040$ in the thousands class, $500$ in the units class:

12\,040\,500 .

The zeros of $040$ are essential: each class (except the leftmost) must show its three digits.

Example 21.3 (How many thousands?)

The number $6\,309\,452$ contains $6\,309$ thousands (everything left of the units class): $6\,309\,452 = 6\,309 \times 1\,000 + 452$ . Asking “how many thousands” is not asking for one digit, but for a whole prefix of the number.

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