Adding to a hundreds number

Students learn to add to a multiple of 100 within 1,000.

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Students learn to add to a multiple of 100.

1.NBT.C.4

Discuss with students that it is important to add numbers to a hundreds number, so you can determine a total.

Show the money on the interactive whiteboard and tell students that they must add to the amounts to compose 100 or 200. The students must determine how many more must be added. Next tell students to decompose the given numbers. Ask students to write down their answers and hold them up on a sheet of paper or interactive whiteboard.

Start by explaining to students that hundreds numbers always end with zeros in the tens and ones places (00). Then tell students that they can add by counting quantities. Start by counting how many you have, that is the first addend of your addition problem. Next count how many are being added, this is the second addend. When you count the two together, you find the total. Show this on the interactive whiteboard using the blocks and money. Next explain a second type of addition problem. You start by looking to see how many there already are, this is the first addend. Then you look at what the total should be. You then determine how many should be added. You can solve this in different ways. Explain to students that you can add using a number line. You can also turn the addition problem into a subtraction problem. You can also compose the number by adding tens and then hundreds to reach the total. Emphasize that you must look carefully at the addends to determine which method works best for the given problem. Ask students to solve a few problems on their own. Ask them to explain their strategy. Finally show students how to solve a story problem. Show that they must first determine which kind of math problem it is, which numbers are important for the problem, to say or write the problem and finally to solve the problem. Ask students to solve a few story problems individually or in groups.

Check that students are able to add to a hundreds number by asking the following questions:

- What is a useful way to add to a hundreds number?

- How do you solve 385 + ___ = 400?__

Students are given problems in which they must add two numbers to a hundreds number with visual support. They must make jumps on a number line as well as simply add the numbers. They are also given story problems and problems in which they must determine what the missing addend is.

Discuss with the students that it is important to be able to add to a hundreds number, so you can determine a total. Show the number line on the interactive whiteboard and ask students to discuss how they would jump to the given total. Then discuss the problem as a class and show some possible jumps on the number line. Next ask students to determine what the number hidden below the paint splatters are. After giving them time to think, ask students to give their answers by turn. Ask them to explain their strategy. Delete the paint splatters away to show the correct answers.

If students have difficulty adding to a hundreds number, they can be supported by making use of a number line as visual support. Remind students that they can make different jumps on the number line to reach the total.

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