# Lesson 12 Estimate and Add

Let’s add decimals and think about whether our answers are reasonable.

## Warm-up Number Talk: 99 Hundredths

Find the value of each expression mentally.

## Activity 1 Use the Standard Algorithm to Add Decimals

Find the value of

. Explain or show your reasoning. Han used the standard algorithm to add decimals. This is Han’s work. Describe what Han did in each step.

Use the standard algorithm to find the value of

.

## Activity 2 Estimate and Find the Value

Which whole number is the sum

closest to? Explain or show your reasoning. What is the value of

? Explain or show your reasoning. Use the standard algorithm if it is helpful. Which whole number is the sum

closest to? Explain or show your reasoning. What is the value of

? Explain or show your reasoning. Use the standard algorithm if it is helpful.

## Practice Problem

## Problem 1

Which whole number is

closest to? Explain or show your reasoning. Find the value of

.