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

  1. Find the value of . Explain or show your reasoning.

  2. Han used the standard algorithm to add decimals. This is Han’s work. Describe what Han did in each step.

    Add. 5 and 61 hundredths, plus, 2 and 53 hundredths, equals. Step 1, 4 hundredths. Step 2, 14 hundredths. Step 3, 8 and 14 hundredths. 

  3. Use the standard algorithm to find the value of .

Activity 2 Estimate and Find the Value

  1. Which whole number is the sum closest to? Explain or show your reasoning.

  2. What is the value of ? Explain or show your reasoning. Use the standard algorithm if it is helpful.

  3. Which whole number is the sum closest to? Explain or show your reasoning.

  4. What is the value of ? Explain or show your reasoning. Use the standard algorithm if it is helpful.

Practice Problem

Problem 1

  1. Which whole number is closest to? Explain or show your reasoning.

  2. Find the value of .