Section B: Practice Problems Add and Subtract Decimals

Section Summary

Details

In this section, we learned that we can use the same strategies and algorithms we used to add and subtract whole numbers to add and subtract decimals.

We learned that it is helpful to estimate a sum before we solve. For example, the sum below is going to be close to or 690.

Add. 6 hundred 21 and 45 hundredths, plus, 72 and 30 hundredths, equals, 6 hundred 93 and 75 hundredths.

We also learned that it is important to make sure the places are aligned when we add and subtract.

Subtract.

We can also estimate that the value of the difference will be about or 550.

Problem 1 (Lesson 11)

Mai and Tyler were playing “Target Number Addition.”

  1. Mai rolled 6 sixes. How close can Mai get to 1 without going over?

  2. Tyler rolled 6 fours. How close can Tyler get to 1 without going over?

Problem 2 (Lesson 12)

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

  2. Find the value of .

Problem 3 (Lesson 13)

Find the value of the expression .

Problem 4 (Lesson 14)

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

  2. Find the value of .

Problem 5 (Lesson 15)

  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 .

Problem 6 (Lesson 16)

Find the value of each expression.

Problem 7 (Exploration)

  1. Kiran finds the value of  with these calculations:

    Explain why Kiran’s strategy works.

  2. Find the difference in a way that makes sense to you.

Problem 8 (Exploration)

Lin is trying to use the digits 1, 3, 4, 2, 5, and 6 to make 2 two-digit decimals whose sum is equal to 1.

  1. Explain why Lin can not make 1 by adding together 2 two-digit decimal numbers made with these digits.

  2. What is the closest Lin can get to 1? Explain how you know.