Subtracting decimals

Subtracting decimals

In this lesson, we will learn:

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

Notes:

• To subtract 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
• A subtraction statement is made of: minuend - subtrahend = difference
• Cross out the blocks that you are subtracting (subtrahend from the minuend), until you've crossed out all matching pairs (subtrahend all crossed out).
• Exchange (or "borrow") from a bigger block if you don't have enough blocks to cross out. One big block can be split into 10 of the next smaller type of block (next place value).

• To subtract decimals, line up the decimal point to make sure you are adding the right place values in the same columns. Exchange (borrow) whenever necessary.
• Sometimes, you will have to write one or more extra zeroes to a number after the decimal point (trailing zeroes) when the minuend/subtrahend don't have the same number of place values.

Lessons

• Introduction
Introduction to Subtracting Decimals:
a)
How to subtract decimals with base ten (block) models

• 1.
Exchanging practice for decimals with block models
Practice exchanging to make more smaller place values. Use base ten (block) models to help.
a)
4 ones + 6 tenths = ___ ones + ___ tenths

b)
Exchange 1 one for 10 tenths:
8 tens + 0 ones + 3 tenths = ___ tens + ___ ones + ___ tenths

c)
Exchange 1 tenth for 10 hundredths:
9 tenths + 1 hundredth = ___ tenths + ___ hundredths

d)
Exchange 1 tenth for 10 hundredths:
2 ones + 0 tenths + 7 hundredths = ___ ones + ___ tenths + ___ hundredths

• 2.
Subtracting decimal block models
Subtract the decimal block models. Give the answer in standard form.
a)

b)

c)

d)

• 3.
Subtracting decimals on a grid
Subtract the decimals by lining up on the grid.
a)
18.7 - 2.3

b)
57.98 - 8

c)
9.2 - 5.4

d)
78.03 - 9.56

• 4.
Subtracting decimals and rounding decimal differences
a)
41.2 - 8.43

b)
62.04 - 31.03

c)
675.92 - 324.7