Unit 5 – Investigation 2.1
”Adding Decimals”
FQ:How do you use place value to add 2 given decimal numbers ?
A:______________________________________________________
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C: ______________________________________________________
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E: ______________________________________________________
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Vocabulary:
Expanded Form
Visual Example
Example
Place Value Opening: Don’t get ripped off!!!!!
Read the problem on page 24 and help Sally Jane and Zeke out. After buying a bag of pretzels for $.89 and
a bottle of cider for $1.97, the clerk charges them $10.87!
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Sally Jane used estimation and found that the cost should be close to $3. How did she likely estimate?
Sally estimated by _________________________________________________________________
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What mistake did the clerk likely make? Write out what the clerk likely added.
Partner Discussion: Look at page 26. How many different distinct values are there?
A. 1) Sort the cards into groups of numbers with equivalent values.
Value:________ Value:________ Value:________ Value:________
Value:________
Value:________
Least 1_________2__________3__________ 4__________ 5_________6._________ Greatest
3) Using a different color, write at least one more equivalent value for each group in the table above.
B. Look at page 27. Isaac and Madeline are using decimal cards to practice finding sums of decimals. Isaac chose 0.074
and 0.0704 and said the sum was 0.0778
Madeline disagreed. She said, “If you use the equivalent expanded form for each decimal, the answer will be
𝟎
𝟏𝟒
𝟒
𝟒
0 + 𝟏𝟎 + 𝟏𝟎𝟎 + 𝟏𝟎𝟎𝟎 + 𝟏𝟎𝟎𝟎𝟎
1) Who is correct, Isaac or Madeline? Explain. ____________ is correct because _______________________
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2) What is the correct answer in decimal form? __________ In fraction form? __________
C. Use of your knowledge of place value and fractions to find the following sums. Rewrite if needed.
1) 70.4 + 7.04
2) 7.4 + 7.04
3) 0.704 + 0.704
4) 0.704 + 7.4
5) Find 2 decimal cards that sum to each value.
a) ______ + ______= 14.44
c) ______ + ______= 7.744
b)______ + ________ = 77.8
d) _____ +________ =0.778
D. Sally Jane said, ”You can add decimals the same way you add whole numbers. You just need to line up the
decimal points to make sure that the numbers with the same place value are added.”
7.4
+ 0.704
8.104
1) How did Sally Jane get each digit in the answer 8.104?
2) Lee Ann said, “It helps to put 2 zeroes after the 4 in 7.4 to be sure that everything lines up right.” Add zeroes
to the addition problem above.
a) Why is 7.4 equal to 7.400?
Challenge: Draw it out visually.
b) Explain how Lee Ann’s suggestion might be helpful.
E. Use your knowledge of place value and fractions to estimate and calculate each sum. Rewrite vertically.
1) 1.1999 +2.02
2) 1.762 + 6.9
3) 0.243 + 0.7
4) 3.47 + 8
F. Look at page 29. Four students calculated the sum 2.561 +15.74 + 92.03 and got various answers. Study their work
to see if any of their sums are correct, identify the errors they made.
The students that added correctly are ______________________. The only difference was ______________________
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___________ is incorrect because ____________________________________________________________________.
___________ is incorrect because ____________________________________________________________________.
G. Describe a systematic procedure or algorithm you can use for finding the sum of two (or more) decimal numbers.