Lesson 7

Round Doubloons

Lesson Purpose

The purpose of this lesson is for students to examine situations where decimal quantities are rounded.

Lesson Narrative

The purpose of this lesson is for students to consider the concept of rounding through the context of weight. There are different reasons why it can be difficult to measure quantities accurately. The quantity can be so large, like the population of Los Angeles, that counting exactly is not realistic. Or the quantity can be a decimal, like the weight of a coin, and then the issue is that introducing new place values can alter the value of the decimal. In practice, the scale used to weigh the coin measures to a specific place value and that means that the actual weight is rounded to this place value. In future lessons, students will round decimal numbers to different place values and look in greater depth at what happens in situations where reported quantities are rounded.

Throughout this lesson, students attend to precision in measurement (MP6). In some cases, such as the scale, they are given how accurately the scale measures weight. In other cases, they are given quantities and determine whether or not they are exact or approximate. 

  • Engagement
  • MLR8

Activity 1: Gold Doubloons

Learning Goals

Teacher Facing

  • Examine accuracy of quantities and relate to rounding.

Student Facing

  • Let's explore rounding with decimals.

Required Preparation

CCSS Standards


Building Towards

Lesson Timeline

Warm-up 10 min
Activity 1 20 min
Activity 2 15 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

What strategy did you anticipate today? Which did you not anticipate?

Suggested Centers

  • Mystery Number (1–4), Stage 6: Decimals (Addressing)
  • Get Your Numbers in Order (1–5), Stage 5: Decimals (Addressing)

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