Fluently Subtracting within 1000
Students will be able to solve subtraction problems within 1,000.
Introduction (15 minutes)
- Invite students to bring their math journals and a pencil to the class meeting area.
- Tell them to place their supplies on the floor next to them.
- Tell the students that today we're going to learn a strategy for solving subtraction problems within 1,000.
- Let the students know that to solve for these problems they must have a strong grasp of place value, which we will do a review of, before proceeding.
- On the board write “Place Value.” Under this term, write the following:
Place: The position of a digit in a number. 10,000s 1,000s 100s 10s 1s Value: The value of the digit in its place
- Ask students what the term place means in regards to a number. As the students share, place the correct definition next to the term.
- Then, ask the students to share what the term value means in regards to a number. As the students share, place the correct definition next to the term.
- Next, come up with a number, for example 14,262, to show the students how to correlate or determine the place and value of specific digits. Make a chart on the board showing these values. For example:
1 4 2 6 2 Place: 10,000s 1,000s 100s 10s 1s Value: 10,000 4,000 200 60 2 (10,000x1) (1000x4) (100x2) (10x6) (1x2)
Explicit Instruction/Teacher Modeling (15 minutes)
- Direct the students’ attention to the board.
- Write a few subtraction problems, within 1,000, on the board, such as 887-498 or 978-683.
- Tell the students that the first thing we want to do is rewrite the problem in place value format, as follows: (800 + 80 + 7) - (400 + 90 + 8).
- Next, tell the students that we will add the numbers, on both sides of the equal sign, based on place value, as follows: (800 - 400) + (80-90) + (7-8).
- With student input, continue to solve the above problem until you find the answer of 389.
Guided Practice/Interactive Modeling (15 minutes)
- Tell the students to pick up their supplies and write down and solve the other problem, 978 - 683, using what’s been termed the "Place Value Method for Subtraction," on the board.
- Ask for volunteers to raise their hands and share with the class the steps involved based on the problem just completed.
- Give the students time to solve the problem.
- As the problem is being solved aloud by the class, write down the steps volunteered by the students on the whiteboard.
- When the problem is done, review it with the class for accuracy. Make sure everyone has the problem written down as a reference for completing their assignment during independent work time.
Independent Working Time (20 minutes)
- Send the students back to their seats.
- Pass out the Subtraction Math worksheets.
- Walk around and observe the students as they work on completing the assignment.
- Monitor the students as they work, making sure the problems are done correctly, in that they are justifying their answers by showing their work.
- During this time, the teacher will ask questions of the students to make sure they understand the concept of subtracting within 1,000 using place value.
- The teacher will also answer questions by the students, to help them clarify any misconceptions they may have.
- Enrichment: Students can be given an additional worksheet if they finish early, additionally, students may start practicing subtracting four-digit numbers.
- Support: Observe and monitor these students more closely. Get involved in helping the students solve the problems. These students would also benefit from the use of manipulatives.
Assessment (10 minutes)
- The students will be assessed based on the comments and feedback from them during the lesson about the assignment and at the conclusion of the lesson.
- They will also be assessed based on the results of the completed problems assigned.
Review and Closing (15 minutes)
- Bring the students back to the class meeting area.
- Ask for volunteers to share their answers and work for the problems assigned.
- As the problems are reviewed in front of the class, the students will check their answers for accuracy.
- After each problem has been checked for accuracy, ask the class if there are any questions or comments on solving for subtraction problems within 1,000 using place value.