Rounding Three-Digit Numbers to the Nearest Ten and Hundred
About this lesson
Children use a number line on the board to decide which ten or hundred a number is closest to. They then show their rounded answers on scrap paper for a set of three-digit numbers. You need a whiteboard, scrap paper and pencils, and it takes about 12 minutes.
- Grade
- 3
- Subject
- Math
- Time
- 12 min
- Prep
- 3 min
Objective
Students will round three-digit numbers to the nearest ten and the nearest hundred and explain their choice using a number line.
Prep
3 min: draw a number line from 340 to 350 on the board and write these 8 numbers beside it: 346, 342, 571, 238, 655, 419, 883, 765
Materials
- whiteboard and marker
- scrap paper
- pencils
Steps
- Point to the number line and mark 346, then ask, 'Is 346 closer to 340 or 350?' Count the jumps together, then explain that numbers ending in 5 or more round up and numbers ending in 4 or less round down.
- Students fold a scrap of paper in half and write 'Ten' on one side and 'Hundred' on the other. Round 342 to the nearest ten together, then sketch a 300 to 400 line and round 342 to the nearest hundred together.
- Read the remaining numbers one at a time. Students write the number rounded to the nearest ten on one side, then hold up their paper when you say 'Show me.'
- Repeat the list, this time rounding to the nearest hundred. After each answer, call on one student to explain which two hundreds the number sits between and which one it is closer to.
- Finish with 655 and 765, which end in 5 or have 5 tens. Ask the class why these round up and agree on the rule together.
Quick Check
Write 482 on the board and have each student write it rounded to the nearest ten and to the nearest hundred (480 and 500) on their paper before putting it away.
Differentiation
Make it easier: Use only two-digit numbers and round to the nearest ten, with a number line drawn for every number.
Make it harder: Give a rounded answer such as 350 and ask students to list every whole number that rounds to it when rounding to the nearest ten.
Good For
- Morning warm-up
- Before lunch
- Supply teacher
- Review
