Lesson: Rounding: Estimating Difference

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Lesson Objective

SWBAT round whole numbers to the thousands place in order to estimate answers to a subtraction problem.

Lesson Plan

Materials Needed: DN Worksheet, white board, dry erase markers, IND Practice Worksheet
Vocabulary: rounding, estimation, actual, rounding off

……….
Do Now (2 - 3 min): On the board the teacher has the following 4 numbers written with different place values underlined. The teacher hands out the half worksheet and asks the students to record the actual number, round to the underlined place value, and identify the place value of the underlined digit.

1. 6, 392
2. 2, 902
3. 4, 093
4. 7, 915

Opening (2 -3 min): Teacher quickly reviews answers to the Do Now and then says, “Today, we are going to further challenge our knowledge of rounding and estimation. Remember, estimation means to give a rough answer that may be a little less or a little more than the actual result. Yesterday we practiced using estimation to find the sum or a product of a problem. By the end of this lesson, you will be able to round whole number to the nearest thousands place in order to estimate the answer to a subtraction problem.”

Direct Instruction (10 min): Teacher begins “Ok! We are going to start today by looking at a word problem together. I am going to show you how estimation can help you find the correct answer and save you time on multiple choice tests.” The teacher has the following problem on the board or a chart and reads it aloud to students.

Example 1: Jared has saved a lot of money for his son’s college. He has saved \$5,802 so far. The college tuition costs \$9,302. Estimate to the nearest thousands in order to find out approximately how much money Jared still needs to save in order to have enough to pay for his son’s college.

Teacher continues, “Ok, this sounds like a lot of work to me. Subtraction of numbers as large as this is not the easiest thing to do, and these problems can sometimes take a while to solve. Now, thinking back to what you learned yesterday about estimating, what would be the first step to solving this estimation problem? [You would round the numbers] Awesome, and the problem already told me to estimate to the nearest thousands. So I want to round both numbers to the thousands. But before I do that, I want to set up my problem. Now, this is going to be a subtraction problem, so I need to decide what number is going to go on top. Do you think the number that is the cost of college or the amount of money that has been saved should go on top of the problem? [The cost of college] Awesome, the cost of college should go on top because that is the total amount of money that Jared wants to save. So, my problem will be set up like this.” Teacher writes the following on the board:

Example 1:

Actual   Estimation

9,302     9,000
-   5,802        ≈     -  5,000
___________ ____________

Teacher continues, “Now that I have set up my problem, the only thing left to do is solve. Who can tell me what 9,000 – 5,000 is? [4,000] Awesome, so Jared needs to save about \$4,000 more in order to pay for his son’s college

Guided Practice (8-10 min): The teacher continues, “Ok, so let’s read and solve this question together using rounding and then estimation!” Teacher has the following problem on the board or a chart. Teacher walks to students through the steps and solves.

Example 2: Monica wants to buy a motorbike that cost \$1,920. She has worked all summer and has saved \$998. Using estimation, decide how much money Monica needs to save in order to buy her bike.

Example 2:

Actual   Estimation

1,920
-       998     ≈     -
___________ ____________

Independent (10 min): The teacher hands out the IND worksheet. Students are asked to complete the worksheet independently and turn it in.

Closing (2-3 min): Teacher calls the attention of the students back toward the front of the class to quickly review the answers to the Independent Practice worksheet/ ask what we learned about.

Lesson Resources

 IND lesson 9 rounding   Classwork 1 DN lesson 9 rounding   Starter / Do Now 1
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