# Lesson 7 Round Doubloons

Let’s explore rounding with decimals.

## Warm-up Notice and Wonder: A Digital Scale

What do you notice? What do you wonder?

## Activity 1 Gold Doubloons

## Problem 1

Until 1728, doubloons weighed 6.867 grams.

After 1728, they weighed 6.766 grams.

You have a scale that measures weight to the nearest tenth of a gram.

Was the doubloon on the scale made before or after 1728?

If you had a scale that measured to the nearest gram, explain why you would not be able to tell what year the doubloon was made based on the weight listed on the scale.

Which doubloons weigh more, the ones made before 1728 or the ones made after 1728? Explain or show your reasoning.

Show the weights of the doubloons on the number line.

## Problem 2

Use the number lines to find which hundredth of a gram the doubloon weights are each closest to.

## Activity 2 Exact or Approximate?

Decide if each quantity is exact or an estimate. Be prepared to explain your reasoning.

There are 14 pencils on the desk.

The population of Los Angeles is 12,400,000.

It’s 2.4 miles from the school to the park.

The runner finished the race in 19.78 seconds.

## Practice Problem

## Problem 1

A $5 gold coin weighs 8.359 grams.

Locate 8.359 on the number line.

A scale measures to the nearest 0.01 gram. What will the scale show for the weight of the coin? Explain or show your reasoning.