Transcript 2.8 Multiplication of Whole Numbers and Decimals

2.8 Multiplication of Whole
Numbers and Decimals
Tuesday, September 24th
In your math notebook, title the page 2.8,
answer the following question.
Estimate the solution to this problem. Write
a number sentences showing you found
your estimate:
3.7 * 6.2=?
Show your work!
Partial Products Method
236*4
Think of 236 as 200+30+6
Multiply each part of 236 by 4
100s
2
x
10s
3
1s
6
4
8
1
+
0
2
2
0
0
4
9
4
4
4 * 200
4* 30
4*6
Add all 3partial products.
Partial Products Method continued
Think of 26 as 20+6
Think of 43 as 40+3
Multiply each part of 26
by each part of 43
Add the 4 partial products.
43*26 = 1,118
20*40
40*6
3*20
3*6
43*26
100s
10s
1s
x
2
4
6
3
+
0
4
6
1
0
0
0
8
1,1
1
8
8
2
Multiplication of Decimals
One way to solve multiplication containing decimals factors is to multiply
as though both factors were whole numbers and then adjust the
product. Specifically:
1.
First make a magnitude estimate of the product.
2.
Multiply the numbers as though they were whole numbers.
3.
Then use the magnitude estimate as a guide to inserting the decimal
point at the correct location in the answer.
For example: 1.3 * 5
1.
Make a magnitude estimate: 1.3 rounds to 1; because 1 *5 =5, the product will
be in the ones.
2.
Ignore the decimal point and mulitply 13 *5 as though both factors were whole
numbers: 13*5 = 65.
3.
Since the magnitude estimate is in the ones, the product must be in the ones.
Answer must be 6.5. 1.3 *5= 6.5
• Watch the following video for extra review!
– If you the link does not work from the PowerPoint, copy and
paste the link!
– http://everydaymath.uchicago.edu/teachingtopics/computation/mult-part-prod/
2.9 The Lattice Method of
Multiplication
Wednesday, September 25th
Lattice Method
Begin with the diagonal in the bottom right-hand corner. The diagonal lines
outside of the lattice squares are the answer spaces.
42*37 = ?
1.
Write 37 above the lattice.
Write 42 on the right side.
2. Multiply 4*7. Then multiply 4*3.
Multiply 2*7. Then multiply 2*3.
Write the answers as shown.
3. Add the numbers along each
Diagonal. Begin with the diagonal
In the bottom right-hand corner.
The sum of the numbers in the
Second diagonal is 15, so write 1 above
2 in the third diagonal. The sum of the
Numbers in that diagonal is 1+2+2=5
4. Answer is shown starting on the upper
left side of the lattice and continuing below
the lattice.
3
7
4
2
3
7
4
2
In class we will work on multiplying
whole numbers and decimals using the
lattice method!
But before then, try it out on your own!
In your math notebook, title the page 2.9,
answer the following question using the
lattice method.
3.7 * 4.2
Show work!
• Watch the following video for extra review!
– If you the link does not work from the PowerPoint, copy and
paste the link!
• http://everydaymath.uchicago.edu/teach
ing-topics/computation/mult-lattice/
2.10 Comparing Millions,
Billions, and Trillions
Thursday, September 26th
In your math notebook, title the page 2.10, answer the
following question.
1.
Explain the strategy you would use to find the
number of minutes in one year.
Show your work!
What is 1,000 times 1 million? 1 billion
(1,000,000,000)
1,000,000,000 = 1,000 *1,000,000
One billion has what relationship to 1 trillion? One
trillion (1,000,000,000,000) is 1,000 time 1 billion.
1,000,000,000,000 = 1,000 * 1,000,000,000
** Count the number of zeros!
What’s the difference between a guess and
an estimate?
Guess= an opinion that you might state
without the support of other
information.
Estimate= based on some knowledge
about the subject and is often called an
educated guess.
Unit 2 Review
Friday, September 27th
Study the following skills:
1.
Add and subtract whole numbers and decimals.
2.
Convert between U.S. customary units of length.
3.
Identify the place value in digits.
4.
Identify multiplication errors
5.
Make magnitude estimates.
6.
Explain usefulness of making an estimate.
7.
Describe probabilities using words or phrases.
8.
Write numbers in expanded notation.
9.
Find the landmarks for a data set.
Use your SRB, Math journal pages, PowerPoint slides, study links, notes
to help you study for the assessment on Monday, September
30th.