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Mathematics · Glossary

What is Classes?

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 millions+309 thousands+452 units,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 4526\,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 1212 in the millions class, 040040 in the thousands class, 500500 in the units class:

12 040 500.12\,040\,500 .

The zeros of 040040 are essential: each class (except the leftmost) must show its three digits.

Example 21.3 (How many thousands?)

The number 6 309 4526\,309\,452 contains 6 3096\,309 thousands (everything left of the units class): 6 309 452=6 309×1 000+4526\,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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