Adding decimals

Adding decimals

In this lesson, we will learn:

  • How to add decimal numbers using base ten (block) models
  • That adding decimal numbers is the same as adding whole numbers, which involves lining up the right place values and regrouping

Notes:

  • To add decimals with base ten (block) models:
    • Remember the three types of blocks used to represent the ones, tenths, and hundredths place values
      • "One whole" or hundred block = ones place value
      • Column (stick or rod) = tenths place value
      • Single square = hundredths place value
Adding Decimals
    • An addition statement is made of: addend + addend = sum
    • Count all of the blocks that you are adding up, altogether
    • Regroup to get to your final answer. 10 of any type of block will regroup into the next bigger type of block.

Adding Decimals

  • To add decimals, line up the decimal point to make sure you are adding the right place values in the same columns. Regroup (carry over) numbers whenever necessary.
    • Sometimes, you will have to write one or more zeroes to a number after the decimal point (trailing zeroes) when the addends don't have the same number of place values.

Lessons

  • Introduction
    Introduction to Adding Decimals:
    a)
    How to add decimals with base ten (block) models


  • 1.
    Regrouping practice for decimals with block models
    Regroup so that each place value only has one digit. Use base ten (block) models to help.
    a)
    17 tenths = ____ ones + ____ tenths
    Adding Decimals

    b)
    4 ones + 12 tenths + 39 hundredths = ____ ones + ____ tenths + ____ hundredths
    Adding Decimals

    c)
    6 ones + 29 tenths + 16 hundredths = ____ ones + ____ tenths + ____ hundredths
    Adding Decimals


  • 2.
    Adding decimal block models
    Add the decimal block models. Give the answer in standard form.
    a)

    Adding Decimals

    b)

    Adding Decimals

    c)

    Adding Decimals


  • 3.
    Adding decimals on a grid
    Add the decimals by lining up on the grid. Regroup where necessary.
    a)
    34.8 + 5

    Adding Decimals

    b)
    4.6 + 2.9

    Adding Decimals

    c)
    41.03 + 5.72

    Adding Decimals

    d)
    35.84 + 6.5

    Adding Decimals


  • 4.
    Adding decimals and rounding decimal sums
    Evaluate. Then, round your answer to the nearest tenth.
    a)
    7.6 + 2.14

    b)
    80.65 + 19.23

    c)
    18.24 + 3.17

    d)
    98 + 38.97