Math automaticity- decomposing 10

Math automaticity- decomposing 10

Math automaticity- decomposing 10

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Math automaticity- decomposing 10

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Students learn to decompose 10 as quickly as possible.


It is useful to be able to quickly decompose numbers so you can divide numbers. If there are 10 students and 2 want a chocolate ice cream, then you quickly know you need 8 more.


Students practice decomposing 10 chickens next to their coop. Drag the chickens into their coop. Then practice decomposing blocks, with a visible decomposition due to color, and decomposing milk packages of all the same color. Ask students how they decompose and see if any students already manage to decompose without counting or have them memorized.


In the introduction the number 10 is shown with all its decompositions shown on a rekenrek and using the arrow between number bonds. Students can also participate on their own rekenreks with the decompositions. Discuss that the numbers in a number bond can always be switched and you can draw lines between the number bond pairs. Use the hourglass to encourage students to answer as quickly as possible. Each decomposition is given 3 seconds on the hourglass. If more (or less) time is needed the time can be modified.

To check that students understand decomposing 10 as quickly as possible you can ask the following questions:
- What does decomposing a number mean? (breaking it down into two parts that equal the first number)
- When is it useful to decompose 10 of something?
- Can you give two decompositions of 10?

Guided Practice

Students get a set of 10 which can be decomposed in 5 ways. Students fill in the missing number as quickly as possible. Their timer counts how long it takes them and the matches it to the target time.


Emphasize that it is important to quickly be able to decompose 10 to know how much you still need or how much you still miss of something. Ask students to come up with examples of these situations. Practice decomposing 10 as quickly as possible to check that they understand decomposing 10 as quickly as possible.

Teaching Tip

Allow students who have difficulty decomposing 10 write down all possible decompositions of 10 in a number bond chart to use as reference while working on the exercises. If students have trouble with decomposing, they can use manipulatives to help visualize the process.

Instruction materials


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