Checking for Reasonableness: Multiplying Decimals
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Subject Area: Mathematics (B.E.S.T.) | Grade Level: 5
Lesson Length: 15 minutes or less
Keywords/Tags: decimals, multiply decimals
Lesson Description: With this lesson, students will be multiplying decimals in real-life scenerios.

  • MA.5.M.2.1 Solve multi-step real-world problems involving money using decimal notation.
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Video : NumberRock: Multiplying Decimals
Instructions: This video does have to be viewed on YouTube. Just click the link that takes you to YouTube and then come back to this page.
Description: Multiplying Decimals and thinking about the reasonableness of the answer.
Forum : What does reasonableness mean?
Instructions: Read the prompt. You can answer with a definition in your own words or give an example of reasonableness.
There are no forum posts.
Description: The NumberRock video mentioned the term "reasonableness". They reflected upon their answer to determine if it was reasonable. Define reasonableness (in terms of math) in your own words. How do you know if an answer is reasonable?
Reading : Reasonableness
Instructions: Please read the following article as many times as needed before starting to go through the rest of the lesson pages. Understanding the content of this passage is very important since the following lesson activities will be all about this content. Feel free to print if needed.

Let's break down this word: reason/able/ness We know both prefixes - ness means "state of" and -able means "able to or can do". So, reasonableness means the state of being able to reason. More simply put - it makes sense! Considering if your answer is reasonable, is simply considering if your answer makes sense! 

If I buy 5 tshirts for $9.99, its reasonable for me to estimate that I will spend about $50. If I multiply and end up with a product of $4.99, it is reasonable for me to think I missed something in my calculations. 

When solving any math equation, it is easy to make silly mistakes. Always double check the reasonableness of your answer! 

Quiz : Multiplying Decimals Quiz
Instructions: Please complete this quiz by choosing the correct answer for each question. You can take this quiz as many times needed.
Question #1
Liz bought 8 bags of candy for $9.34. She is estimating that she will pay about $80. Is she correct?
Question #2
Susan retued 13 books to the library late. There was a .89 fee for late books, per book. She looks in her purse hoping to find a few dollars. She is estimating her fine to be about $1.30. Is she correct? 
Question #3
Janice stopped at Zippy gas station. Thier gas was listed for only 2.89 per gallon. Her car has an 11.5 gallon tank. She is excited because gas should only cost her about $36.00! Is she correct? 
Question #4
Noah had .5 of his birthday cake leftover after his party on Saturday. When he got home from school on Monday he at .5 of the cake that was left. His mom asked what he ate when he got home from school. Noah said he ate about .25 of his birthday cake. Is he correct?
Question #5
Kylie bought some grapes for $2.89 a pound. The grapes weighed 2.3lbs. About how much will Kylie pay for grapes (estimate)? 
Question #6
(Refer to the question above) Kylie brought a five dollar bill with her to the store. Does she have enough?
Question #7
(Refer to question #5 and #6) How much will the grapes cost Kylie? 
Question #8

3.8 x 7.5 = 

Question #9

5.2 x 0.45 =

Question #10
68 x 0.72 =
Description: Practice thinking about the reasonableness of your answer.
Resources : How to check your work
Instructions: Please see additional external resources below. Feel free visit each link to learn more about this lesson.
How to Check your Work