# Lesson: Estimation Techniques: + / - Computations of 3 Digit Numbers

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

SWBAT use estimation techniques to solve whole number computations (addition /subtraction) up to 3 digit numbers.

### Lesson Plan

Materials Needed: DN worksheet, dry erase markers, white board, pencils, IND Worksheet.
Vocabulary: rounding, estimation, actual, rounding off, decimals, place value, difference, sum

……….
Do Now (3 -5 min): Teacher gives each student a DN worksheet and asks them to complete the work as quickly and quietly as possible. DN today is a quick multiplication drill to freshen up on mental math facts.

Opening (2 -3 min): Teacher quickly reviews answers to the Do Now and then says, “Yesterday we reviewed regrouping as a strategy to estimation. Today, we are going to put what we have learned to the test. We have learned that we can use rounding and regrouping to estimate approximate answers. By the end of this lesson, you will be able to use either estimation technique to solve whole number computations (addition /subtraction) up to 3 digit numbers.”

Direct Instruction (10 min): Teacher begins “Ok! Let’s quickly review front end rounding and regrouping! The two steps to front end rounding are on the board.” Teacher should write the following on the board.

1) Add the digits of the two highest place values
2) Insert zeros for the other place values

The teacher continues, “Who would like to read them for me? Who can give me an example of when they used this technique, and in class example will do [Answers will vary]. Great! Now who can tell me what regrouping is? Why is it helpful when looking for an approximate answer? [Answers will vary]. Great job everyone! We can now begin adding and subtraction our 3 digit numbers for today. Let me show you how I want you to work on these problems today. Watch as I do this one on the board. ” Teacher writes the following on the board:
891 + 561 =
Which Strategy?: Rounding
900 + 600 = 1,500

Teacher says, “Ok, why do you think I picked rounding as my strategy? I picked it because it was the fastest option. If I regrouped I would have had to do more mental math, so I went with the easiest option to get the estimate or approximate answer. I am going to complete one more problem, as you watch and then we will try some together.” Teacher writes the following on the board and explains the thought process out loud as he/she writes:

825 – 431 =
Which Strategy?: Rounding
800 – 400 = 400

"Again, rounding was the faster strategy. I did that problem in less than 10 seconds. My challenge to you during group work is to not spend more than 10 seconds on each problem. You will be completing problems almost identical to the ones I completed on the board. I want you to specify which strategy you used to get your estimate or approximate answer. Let’s get started.”

Guided Practice (8-10 min): Teacher says, “Now, I will give you five problems to do together in groups of 2 or 3 on your own paper. Help each other as you work, because in a minute I will have you do some problems on your own.. Let’s get started.” Teacher writes the following on the board and gives each student time to solve the problems together in small groups.

1. 891 + 237 =
Which Strategy?: _____________________
Solve:__________________________________

2. 902 – 789 =
Which Strategy?: _____________________
Solve:__________________________________

3. 371 – 231 =
Which Strategy?: _____________________
Solve:__________________________________

4. 548– 431 =
Which Strategy?: _____________________
Solve:__________________________________

5. 912 + 621 =
Which Strategy?: _____________________
Solve:__________________________________

Independent Practice (5 -8 min): The teacher reviews the answers to the Guided Practice with the class and then passes out the IND practice worksheet.

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/ ask what we learned about.

### Lesson Resources

 IND lesson 7 estimation   Classwork 607 DN multiply single digit   Starter / Do Now 373
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