Lesson 15 Estimate and Subtract

    • Let’s use place value to subtract decimals.

Warm-up Number Talk: One and Five Tenths

Find the value of each expression mentally.

Activity 1 Revisit the Algorithm

  1. Find the value of . Show your reasoning.

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

    Subtract. 8 and 53 hundredths, minus, 2 and 7 tenths, equals. Step 1, 3 hundredths. Step 2, 83 hundredths. Step 3, 5 and 83 hundredths.

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

Activity 2 Estimate and Subtract

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

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

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

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

Activity 3 Compare Calculations to Evaluate a Difference

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

  2. Elena and Andre found the value of . Who do you agree with? Explain or show your reasoning.

    Elenas and Andres subtraction algorithms and reasoning.

Practice Problem

Problem 1

  1. Here is how Elena found the value of .

    Subtract. 15 and 37 hundredths, minus, 8 and 19 hundredths, equals, 7 and 18 hundredths.

    Explain Elena’s calculations and the meaning of the 15 above the 5 and the 17 above the 7 in 15.37.

  2. Use Elena’s algorithm to calculate .