Lesson 8: I can fluently multiply multidigit whole numbers using the standard algorithm and using...

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5th Grade Module 2 – Lesson 8
Lesson 8: I can fluently multiply multidigit whole numbers using the standard algorithm and using estimation to check
for reasonableness of the product
5th Grade Module 2 – Lesson 8
State in Exponential Form
102
Say the base.Say the exponent.
Say 10 squared as a multiplication
sentence starting with 10
10 x 10 = 100
Say it as a number sentence without
using a multiplication
sentence
10 squared = 100
5th Grade Module 2 – Lesson 8
State in Exponential Form
103
Say the base.Say the exponent.
Say 10 to the third as a multiplication sentence starting
with 10
10 x 10 x 10 = 100
Say it as a number sentence without
using a multiplication
sentence
10 to the third = 1000
5th Grade Module 2 – Lesson 8
State in Exponential Form
104
Say the base.Say the exponent.
Say 10 to the fourth as a multiplication sentence starting
with 10
10 x 10 x10 x 10 = 10,000
Say it as a number sentence without
using a multiplication
sentence
10 to the fourth = 10,000
5th Grade Module 2 – Lesson 8
State in Exponential Form
105
Say the base.Say the exponent.
Say 10 to the fifth as a multiplication sentence starting
with 10
10 x 10 x 10 x 10 x 10 = 100
Say it as a number sentence without
using a multiplication
sentence
10 to the fifth =
100,000
5th Grade Module 2 – Lesson 8
State in Exponential Form
107
Say the base.Say the exponent.
Say 10 to the seventh as a
multiplication sentence starting
with 10
10 x 10 x 10 x 10 x 10 x 10 x
10= 100
Say it as a number sentence without
using a multiplication
sentence
10 to the seventh = 10,000,00
0
5th Grade Module 2 – Lesson 8
Multiply Using the Area Model with a Zero in One Factor
287 x 64 ≈ ___ x ___ = ____300 60 18,000
On your boards, write the multiplication sentence rounding
each factor to arrive at a reasonable estimate of the product.
5th Grade Module 2 – Lesson 8
Application Problem
Erin and Frannie entered a rug design contest. The rules stated that the rug’s dimensions must be 32 inches x 45 inches and that they must use rectangles. They drew the following for their entries. Show at least 3 other designs they could have entered in the contest and calculate the area of each section and the total of your rugs.
5th Grade Module 2 – Lesson 8
5th Grade Module 2 – Lesson 8
314 x 236
Round each factor to estimate the
product.
Turn and talk.
Multiply your rounded factors to
estimate the product.
What is 300 x 200?
300 x 200 = 60,000
Express 60,000 as a multiplication expression with an exponent.
6 x 104
I noticed that we rounded both of our factors down to the nearest hundred.
Will our actual product be more than or less than our estimated product?
The answer should be more because our actual
factors are more than what we rounded to!
Solve using the standard algorithm.
Look back at our estimate. Is our answer reasonable?
5th Grade Module 2 – Lesson 8
1,882 x 296
Round each factor and estimate the product.
Will the actual answer be greater than or less than
your estimate?
2,000 x 300
Work independently to solve for the actual answer.
Is the product reasonable?
5th Grade Module 2 – Lesson 8
4,902 x 408
Find the estimated product for this
problem.
Let’s read the estimated multiplication sentence
without the product.
4,902 x 408 is about as much as 5,000 x
400
Some of you estimated the product to be 200,000.
What is the error?
We cannot simply count the zeros! You must
think about your units!
Should our actual product be more or less than our actual
product? Turn and talk!
We rounded one factor up and one factor down. We can’t really tell but it
should be close!
5th Grade Module 2 – Lesson 8
Get Ready to Complete theProblem Set on Your Own!
Complete Pages 2.B.75  2.B.76 You will have 10 minutes to work.
Try your Best!
5th Grade Module 2 – Lesson 8
Debrief•How can estimating before solving help us?
•Look at Problem 1(b) and (c). What do you notice about estimated products? Analyze why the estimates are the same but the products are so different.
•How could the cost of the chairs have been found using the unit form mental math strategy?
5th Grade Module 2 – Lesson 8
Debrief•In Problem 3, Carmella estimated that she had 3,000 cards.
•How did she most likely round her factors?
•Would rounding the number of boxes of cards to 20 have been a better choice? Why or why not?
•Do we always have to round to a multiple of 10, 100, or 1,000? Is there a number between 10 and 20 that would have been a better choice for Carmella?
5th Grade Module 2 – Lesson 8
Debrief
•Can you identify a situation in the real world where overestimating would be most appropriate?
•Can you identify a situation in the real world where underestimation would be most appropriate?
5th Grade Module 2 – Lesson 11
EXITTICKETPage 2.B.77