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3rd Grade Math Lesson

Mission Control: Rounding to the Nearest 10 and 100

Shared by A STEM Educator

3rd GradeBuilding Thinking ClassroomsCCSS.MATH.CONTENT.3.NBT.A.150 min
Learning Objective

Students will round 2- and 3-digit numbers to the nearest 10 and 100 by identifying bounding multiples, locating the exact midpoint, and using relative distance on an open number line to determine the closer benchmark.

Lesson Overview

Students act as Mission Control navigators guiding a deep-space probe to the nearest fuel waypoint. Using open number lines and midpoint benchmarks — not digit rules — they discover that rounding means finding which bounding multiple is closer. Tasks progress from 2-digit rounding to reverse-engineering mystery numbers.

Materials

  • Vertical non-permanent surfaces (whiteboards, chart paper on walls)
  • Dry-erase markers (1 per group)
  • Erasers or socks
  • Random group generator (cards, sticks, app)
  • Printed open number line strips (optional backup)
  • Projector for Desmos interactive

Scaffolded Task Progression

1Task 1
The probe is at position on the number line. The two nearest fuel waypoints are at the nearest tens. On your whiteboard: (1) Draw an open number line and mark the two bounding tens around . (2) Mark the exact midpoint between them. (3) Is closer to the lower ten or the upper ten? How far away is each waypoint? Which waypoint does the probe dock at?
2Task 2
The probe is now at position . On your whiteboard: (1) Draw an open number line and mark the two bounding tens around . (2) Mark the exact midpoint. (3) Which waypoint is closer? How do you know using distance? Which ten does round to?

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