At a Glance...

B1.4 Read, represent, compare, and order decimal numbers up to thousandths, in various contexts.

Activity 1: Who's Faster?

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Grade 6 students run a 100 metre race at recess. The race is timed in seconds, down to thousandths. The results are below. How can we determine the order of speed of the students?

Student 1: 18.248 seconds

Student 2: 18.332 seconds

Student 3: 19.561 seconds

Student 4: 17.199 seconds

Example

By comparing and ordering the thousandths of a second, it is possible to determine that Student 4 has the fastest speed, Student 1 has the second fastest speed, Student 2 has the third fastest speed and Student 3 has the fourth fastest (or lowest) speed.

Activity 2: What About Dewey?

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This activity allows students to expand their knowledge of decimal numbers by reading and comparing Dewey classification indices.

There are several classification systems. The one used for the classification of books in a library was developed by the American Melvil Dewey and is based on the decimal system. In this system, all books are classified, according to their subject, by a number composed of several digits called the index (Dewey classification index), followed by letters and numbers (author's number) that define each book more precisely. This system ensures that all books on the same subject are grouped together in the same section of the library. The Dewey Classification Index divides all subjects into ten broad classes as follows:

Note: A class may be found under various similar names from one source to another. For example, class 700 is sometimes named Arts and Entertainment, Fine and Decorative Arts, or Arts, Recreation and Sports.

Each of the numbers following the hundreds position corresponds to a subdivision that further specifies the subject of the book within the broad class. For example, the index for a book on soccer is 796.334 because of the following subdivisions:

Note: The Dewey classification system uses a decimal point to provide more specific subject groups beyond the ten broad classed. Also, the index of a book does not always contain 6 digits.

It is not necessary for students to know the Dewey Decimal System in detail, but the ability to compare decimal numbers represented in the subscripts will help them more easily find a book on the shelves of a library since books are placed in ascending order of subscript. For example, a book with the index number 611.43 is placed after book 611.34. To locate, for example, the book with the index 611.347, students must first discover the section of 600 (Technology) in the library, then locate where the volumes are in 610, then the subsection 611. Students continue in this manner with each of the decimals 3, 4 and 7. Each of the numbers that make up the left-to-right clue narrows the search area. It is possible that several books have the same clue. In this case, the author number will be used. All libraries that use the Dewey System classify books according to the indexes.

As an activity, bring several books from the school library to class and have students place them in the order they would be placed on a shelf. Students should then use their ability to compare decimal numbers and place them in order of increasing index. Afterwards, invite the class to go to the school library and ask students to place books in the correct order on the shelves.

Source: translated from Guide d’enseignement efficace des mathématiques de la 4^e à la 6^e année, Numération et sens du nombre, Fascicule 3, Nombres décimaux et pourcentages, p 111-113.