Addition to 100 making ten

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Students learn to add to 100 making ten.

2.NBT.B.5

2.OA.A.1

Discuss with students that it is important to be able to add to 100 to be able to determine how many you have together.

Show the money amount on the interactive whiteboard and say that it must be added to to total 40. Students must determine how many more dollars are needed. Repeat this exercise with the stamps. Then ask students to decompose the given number. Ask students to write their answers and hold up their paper to check their answers. Erase the grey box to check the answer.

Start by explaining that tens always end in 0. Next explain that you can add by counting amounts. You first count how many you have, that is your first addend. Then you count how many are being added, that is your second addend. When you add them together, you get the total, or sum. Show this on the interactive whiteboard with the problems with dollars and cookies to discuss how to solve the problems. Check that students are able to add with the exercises with blocks and eggs. Ask students how they determined the total of the problem. Then practice with another kind of addition problem. Tell students that you can also count on to determine the total. Practice counting how many you have, and counting on with the second set of objects. Check that students understand counting on with a few exercises. Next discuss that you can solve addition problems in different ways. Say that you can use a number line, but you can also turn it into a subtraction problem. Say that you have to look closely at the problem to determine what the easiest way to solve it is. Ask students to solve a few problems and ask them how they calculated. Finally show them how to solve a story problem. Have them determine what kind of problem it is, which numbers are needed for the problem, to say or write the problem and then to solve for the answer.

Check that students can add to 100 making ten by asking the following questions:

- What do you look at when you want to solve a story problem?

- How do you calculate 23+7 and 48=__=70?__

Students start by adding with visual support of a number line. They then must determine what the missing addend is, and finally students are asked to solve a story problem.

Discuss with students that it is important to be able to add to 100, so you can determine how much you have in total. Show a number line on the interactive whiteboard and ask students to discuss in pairs how they would solve the addition problem. As a class discuss which steps you can take on the number line to solve the problem. Then ask students if they can fill in the blanks. Give students time to discuss and determine the answer and then ask a student in class for the answer. Ask them how they reached that total- to explain their thinking. Show the answer to check their work.

Students who have difficulty adding to 100 can use the number line as support. Make sure that they understand that they can take different steps (or jumps) on the number line. They can also be supported by practicing making ten, to make the next steps on the number line easier.

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