Subtracting from Multiples of 100
Students will be able to subtract from multiples of 100.
- Gather the students together in a comfortable area.
- Write 100 on the whiteboard. Ask students to turn and talk to an elbow partner, explaining what they see. Do not tell them the number orally prior to having them discuss with their partners.
- Allow a few students to share their ideas and record them on the whiteboard.
- Sketch a picture of a hundred block on the board using a square and show students the tangible hundred block.
- Explain to the students that today they will be learning about Subtracting, or taking away, multiples of 100. Elaborate that MultiplesOf 100 are numbers that can be produced, or made, by adding 100 to another number.
Explicit Instruction/Teacher modeling(10 minutes)
- Play the Counting By 100 to 1000 song.
- Write down 100, 200, 300, 400, 500, 600, 700, 800, and 900 on the whiteboard. Explain to the students that they will only be exploring multiples of 100 up to 900 today.
- Read each of the numbers aloud and have students chorally chant the numbers back to you.
- Ask students what all of the numbers have in common. Allow them to talk to an elbow partner prior to having students share their ideas aloud with the rest of the class. Jot down their ideas on the whiteboard. Ideas may include: all of the numbers have two zeros, the numbers on the left go up by one, the numbers are multiples of 100, they are all big numbers, etc.
- Write down 500 – 200 = ____On the whiteboard.
- Explain to the students that you want to figure out how many ants live on a huge ant farm in your yard. Say, "I had 500 ants, but 200 ants moved to my neighbour's yard. I wonder how many ants I have left on my ant farm in my yard now?"
- Elaborate how to subtract 200 from 500, using the standard algorithm starting in the ones place and making your way to the hundreds place.
- Repeat the process again choosing another engaging and relevant story problem. Have students help you detail the process of subtracting using sequencing words.
Guided practise(10 minutes)
- Project the Subtracting From Multiples of 100 worksheet on the whiteboard. Review the directions for Part 1 and read aloud the example. Elaborate that it is important for them to understand how to write the multiples of 100 in word, number, and visual form.
- Put students in partnerships and have them finish the rest of Part 1. Rotate around the room as students are completing their worksheets and check for understanding.
- Review student answers and fill in their answers on the Subtracting From Multiples of 100 worksheet you have projected on the whiteboard.
Independent working time(10 minutes)
- Pass out the baggies of the flashcards from Part 2 of the Subtracting From Multiples of 100 worksheet to each partnership along with nine base-ten hundred blocks.
- Explain to the students that first they will match the sketch of base-ten blocks with the correct equation. Next, they will come up with their own equation and sketch and record them on the blank flashcards in their baggie.
- Provide students with an example of a problem on the whiteboard and reinforce that the number they are subtracting from must be larger than the number they are subtracting.
- Have students turn and talk to partners, sharing three of the biggest numbers from Part 1 of their worksheet (e.g. 700, 800, 900).
- Rotate around the classroom as students are matching their equations with the base-ten block sketches. Jot down notes of students who understand the task and students who need further support.
- Encourage students to refer to Part 1 of their worksheet for support.
- Provide students with more difficult subtraction problems with multiples of 100 up to 2,000.
- Encourage students to create more than one set of flashcards with their partners, using blank sheets of paper.
- Allow students to work in a small, teacher-led group during Part 2 of the lesson.
- Remind students to use their base-ten hundreds blocks for support throughout the lesson.
- Collect all of the finished flashcards and bring students together in a seated circle on the floor.
- Tape the large anchor chart on a whiteboard or wall with the heading, "We Can Subtract From Multiples of 100."
- Lay all of the flashcards out on the ground and allow student volunteers to try to match the equations with the base-ten sketches. Remind them to choose flashcards that are not their own.
- Have students explain their reasoning and clarify any misconceptions. Glue or tape the matching flaschards on the large anchor chart to refer to for future lessons on subtracting from multiples of 100.
Review and closing(3 minutes)
- Review important vocabulary words from the lesson, such as subtraction and multiple.
- Ask students to answer one of the following discussion questions/prompts as a quick whip-around-pass:
- What are multiples?
- Detail the process we can use when subtracting multiples of 100.
- Is it easier or harder to subtract when there are zeros in the ones and tens place?