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Rounding with Number Lines
Students will be able to round whole numbers to the nearest thousand.
- Draw a number line on the board that shows numbers zero through 10. Ask students to identify the number that is halfway in between zero and 10 (five). Then point at the number two and ask, "Is this closer to zero or 10?" Repeat with several numbers on the number line.
- Tell students that today they are going use number lines to round numbers to the nearest thousand.
Explicit Instruction/Teacher modeling(10 minutes)
- Review the definition of rounding (making a number simpler but keeping its value close to what it was) and the purpose of rounding (giving a less specific or approximate amount that is easier to think about or count).
- Write a four-digit number on the board (like 2,357) and explain that you are going to round to the nearest thousand. Underline the digit in the thousands place (this is the place value that you are rounding to).
- Draw (or display) a number line divided into tenths, but leave it unlabeled. Point out that the number 2,357 is greater than 2,000 (write 2,000 on the first number line marker) and less than 3,000 (write 3,000 on the last number line marker). Explain that, since we are rounding to the nearest thousand, the number will be rounded to either 2,000 or 3,000 because it falls somewhere in between.
- Ask students, "What is halfway between 2,000 and 3,000?" (The answer is 2,500.) Label the halfway point and explain that we can use the halfway mark on the number line to help us figure out if our number is closer to 2,000 or 3,000 (i.e., a number that is to the left of the halfway point is closer to 2,000 and a number that falls to the right of the halfway point is closer to 3,000).
- Label a point on the number line to designate 2,357. Ask students, "Is this number closer to 2,000 or 3,000?" Then draw an arrow from the point to the marker reading 2,000.
Guided Practice(10 minutes)
- Hand out a page of blank number lines to each student.
- Write a number on the board (e.g., 6,702) and guide students through another example, this time having them make a number line as you guide them through it.
- Write a number on the board (e.g., 4,458) and have students work with a partner to make a number line.
Independent working time(10 minutes)
- Write three more numbers on the board and have students independently make number lines to round each number to the nearest thousand (e.g., 1,936; 5,527; 8,196).
- Circulate and offer support as needed. Go over the number lines with the class when finished.
- Have students review rounding with smaller (two or three digit) numbers.
- Provide additional examples during guided practice.
- Have students round a single number to multiple place values (i.e., round 9,481 to the nearest ten, hundred, and thousand).
- Have students apply the skills learned to solve addition word problems (i.e., if Jenny has 2,319 stickers and Lenny has 5,827, about how many do they have altogether?).
- Hand out index cards or scraps of paper to each student and instruct them to write a number greater than 1,000 and less than 10,000.
- Collect all the student generated numbers. Then, let each student blindly choose a number.
- Instruct students to round the number they picked to the nearest thousand by drawing a number line (using one of their remaining blank number lines).
- Collect your students' work and check for understanding.
Review and closing(10 minutes)
- Hand out pre-made sticky notes that are labeled with numbers to make human number lines (e.g., 11 sticky notes labeled 1,000 to 2,000, counting by hundreds). Color code the labeled sticky notes so that all yellow sticky notes will form one number line and blue sticky notes will form another (with different numbers, like 4,000 to 5,000).
- Have all students with yellow sticky notes come to the front of the room and work as a team to form a number line (wearing their sticky notes on their shirts).
- Then call out a number (e.g., 1,478) and have all the students in the number line point in the direction it will be rounded. Repeat with a few numbers.
- Call up the next group and repeat the exercise. If needed, have some students participate in more than one group so that all groups can make a complete number line and all students have a turn.