Subtraction to 10 with one more or one less

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Students learn to subtract numbers to 10 in which they need to add one more or take one away.

1.OA.C.6

It is important for students to learn how to subtract with one more or one less. If you know when you need to add one more or take one away, you don't need to recalculate sets of numbers.

Show the flags on the interactive whiteboard and ask students to count them out loud. Repeat this counting forward and backward. Next show the numbers on the interactive whiteboard and ask students what the neighbor numbers of the given numbers are. Circle the neighbor numbers in the same color as the given number.

Show students 9 colored pencils. One group of 6 colored pencils and a second group of 3. Ask students how many pencils there are. Now ask the students what happens if you remove one colored pencil from the group of 3. How many colored pencils do you have now? Repeat this a few times with different divisions in which the change is always one more or one less. Next discuss subtraction with one more and one less using the ice cubes as visual support. Show students that there were seven ice cubes. Four have melted. As a result there are three frozen ice cubes left. Discuss the other ice cube examples. Ask students if they notice anything about the problems you've discussed. The second number of the problem goes up by one each time. It is not always possible to have images to support math problems, sometimes you only see the numbers. You then compare the subtraction problems. If the first number in the second problem is one more than the first number in the first problem, then the difference is also one more in the second problem. Show the subtraction problems on the interactive whiteboard and ask students if they can determine the answers. Also ask them the steps they took to solve the second and third subtraction problems. Did they do the calculation again, or did they just add one more? Tell students that when the second number in the second problem is is one more than the second number in the first problem, that the difference is one less. Practice subtraction problems demonstrating this.

Next show students the ice cubes on the interactive whiteboard and determine as a class that there are 6 ice cubes. Two have melted, so there are four frozen ice cubes left. Discuss the rest of the ice cube examples. Ask students if they notice anything about the subtraction problems. They should notice that the first or second number in the subtraction problem is one less every time. It is not always possible to have images to support math problems, sometimes you only see the numbers. You then compare the subtraction problems. If the first number of the second problem is one less than the first number of the first problem, your difference is also one less. Show students some subtraction problems on the board and ask students what the answer should be. How did they determine the answers? Did they recalculate or did they just take one away? Tell students that when the second number in the second problem is one less than the second number in the first problem, that the difference is one more. Practice subtraction problems demonstrating this. Then ask students how they determined the answers. Did they recalculate or did they simply add one more? Ask students to write the answers to the following subtraction problems on a sheet of paper. At the end ask students to hold up their answers so you can check their work.

Check that students are able to subtract numbers to 10 with one more or one less by asking the following questions:

- What do you need to look at to determine if a problem gets one more or one taken away?

- Calculate the following: 9 - 3 = and 9 - 4 =

- Calculate the following: 6 - 2 = and 5 - 2 =

Students first practice subtraction with one more or one less with a set of two subtraction problems. Then they are asked to subtract with one more or one less with a set of three subtraction problems.

Discuss with students that it is important to be able to subtract numbers to 10 with one more or one less so you can easily solve sets of calculations. Show subtraction problems on the interactive whiteboard and have students come up with subtraction problems that require one more or one less. Next have the students solve the given subtraction problems on a sheet of paper. Have them hold up their papers so you can check their work. You can erase the grey squares to show the answers.

Students who have difficulty subtracting with one more or one less can be supported by the use of manipulatives such as MAB blocks. Have them first set out the total number of blocks. Then ask students to take away the blocks represented by the second number of the subtraction problem. Then have them set out the blocks for the same problem, but with one more or one less. Repeat this for both.

Optional: MAB-blocks or other manipulatives

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