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DECIMALS: EQUIVALENCE, ROUNDING AND ESTIMATING

Decimals expand our number system. One type of decimal problem that you have already worked with is money.  The amount of $4.23 is also the decimal, 4 and 23 hundredths.  We’ll take a look at equivalent decimals and decimal squares to begin to explore the world of decimals. 

Looking at a number line helps to round a decimal number.  We’ll look at a number line that includes decimals and see how to round decimals. 

Estimating will give an approximate amount for the actual amount needed in the problem.  We’ll look at estimating a money problem to see how estimating with decimals can be useful.

Decimal Squares

Equivalent Decimals Using Decimal Squares

 

Here is a model of 2.4 (2 and 4 tenths) using decimal squares.


Here is a model of 2.40 (2 and 40 hundredths) using decimal squares.


Through the models you can see that 2.4 and 2.40 represent the same amount. 

 

2.4 = 2.40


1 tenth strip has 10 hundredth squares in it; thus there would be 40 hundredth squares in 4 tenth strips.

 
Rule:  To make equivalent decimals, you may add on zeros as needed.  The zeros do not change the value of the decimal, just its appearance.

 

2.4 = 2.40 = 2.400

 

2 and 4 tenths equals 2 and 40 hundredths equals 2 and 400 thousandths

or

Rounding Decimals

Estimating with Decimals

 
Jonathan's mother is planning a trip to the grocery market.  She has $20 to spend.  She wants to estimate the cost of her bill so that she will stay within her budget.  She jots down the items with an approximate price:  cereal ($3.95), bread ($0.89), milk ($2.39), chips ($2.50), lunchmeat ($3.79), apples ($1.99), potatoes ($2.69), cottage cheese ($2.19) and butter ($2.49).  She decides to round to the nearest $0.50 to get a more accurate estimate. Does she have enough money?

 Estimating Decimals
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Below are additional educational resources and activities for this unit.
 
Click on the icon to find and practice topics for this unit.
 
Unit 14 Rounding Decimal Numbers Worksheet
 
Click here to watch a video about deimals.
 
Unit 14 Shading Grid Activity