Lesson: Rounding: Estimating Sum and Product

Tara Smith E.l. Haynes Pcs Washington, DC
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Lesson Objective

SWBAT round whole numbers in order to estimate to find a sum or product.

Lesson Plan

Materials Needed: DN Worksheet, white board, dry erase markers, pencils, and IND 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 record the actual number, round to the underlined place value, and identify the place value of the underlined digit.
1. 56,901
2. 128,630
3. 782,901
4. 76,521
Opening (2 -3 min): Teacher quickly reviews answers to the Do Now and then says, “Today, we are going to put our knowledge of rounding to the test. We are going to begin estimation. I went over what estimation was on the first day of this unit. Estimation means to give a rough answer that may be a little less or a little more than the actual result. Yesterday we rounded to the hundred thousands place, so today we will begin estimating by rounding numbers to the thousands place and then estimating the answer. By the end of this lesson, you will be able to round whole number to the nearest thousands place in order to estimate a sum.”
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: 58 people are invited to the party; you are going to the store to buy supplies.  You figure that for each person you need two cups, two plates, and three napkins.  How many cups, plates, and napkins do you approximately need?
Teacher continues, “Ok, this sounds like a lot of work to me. I know I need to multiple 58 (the number of people) by the number of things I need, so that seem like 3 multiplication problems to me. And I would much rather do one. I can use estimation here to help me check my answer. I am going to start my rounding the number of people invited. Who can tell me what I should round that to? [60]. Great job! Now, I can just add the number of cups, plates and napkins together so I only have to multiple once. How much would that be? [7]. Great! Now I have one problem to multiple, which will give me an estimate on how much to buy.” Teacher writes 60 x 7 = [420] on the board and solves. Teacher continues, “Ok, so I know my estimated answer. Lets compare it to the actual answer, which would be 58 x 7 = [406]. See how close the estimation was? You could have used that to remove distracter answers from a multiple-choice question! Alright, that demonstrated why using estimation in a multiplication problem can help us with multiple-choice questions. You might also be asked to use estimation in an addition problem This is important for two reasons, 1) Using estimation with addition can help you make sure you didn’t make a mistake calculating your sum, 2) you will probably be asked to show off your estimation skills on the test in an addition problem. For those two reasons, Watch as I show you how to complete rounding and then estimating the sum.” The teacher writes the following on the board/chart. The estimation column should be revealed as the teacher rounds the actual numbers and solves.
Example 2:
Actual   Estimation
     6709                        7000
+  4100        ≈                   +   4000
___________ ____________
  10,809                               11,000
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 two problems on the board or a chart. 
Example 3: 92 people are invited to the party; you are going to the store to buy supplies.  You figure that for each person you need two cups, two plates, and three napkins.  How many cups, plates, and napkins do you approximately need?
Example 4: Ms. Tom has saved a lot of money for her son’s college. She has saved $7,802 so far. Her sister has also been saving for her nephew’s college. She has saved $2,341. Estimate to find out approximately how much money they have saved together.
Actual   Estimation
+  2341     ≈     +   
___________ ____________
Independent (10 - 18 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 8   Classwork
DN Lesson 8   Starter / Do Now


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