Lesson: Estimating Differences with Whole Numbers
Lesson Objective
Lesson Plan
State Standard: 
5.NSOE.23 
Standard Name: 
Estimating Differences 
Objective: 
SWBAT estimate differences of whole numbers by choosing the most reasonable place to round to and then subtracting. 
Essential Question: 
When are estimating and rounding used in real life situations? 
Word Wall Words: 
Estimation Difference

Do Now: 
Estimate the sum of each problem.

Opening: 
Remember yesterday we talked about estimating the answers to addition problems to make it easier. Today we are going to continue estimating, but we are going to look at subtraction problems. Remember, in rounding, you are usually given a specific place to round to, like the tenths or the tenthousands place. However, in estimation, we get to pick where we will round to. We decide this based on what will make the number easiest for me as a mathematician. Today, we are going to estimate differences of subtraction problems. 
Direct Instruction: 
We started the year 137 pencils. So far we have used 49. About how many do we have left?
One way I could solve this is to just write out the numbers and subtract them. However, since the problem is asking us “about,” that word tells me that it is okay to estimate. So what can I do to make this problem easier? Estimate (NOT guesstimate!)
Just by looking at my numbers, I see that I am working with 2 different place values here. My first number goes out to the hundreds place, and my second number only goes to the tens place. So I’m going to first try rounding 49 to 50, and then I really have two possibilities for 137. I could either round it to the tens place, which would be 140, or I could round it to the hundreds place, which would be 100. Even though those are both correct estimations, which one is going to give me a more accurate estimation? 140. So, my problem is 140 – 50.
Remember, if I wanted to check to make sure this is reasonable, I can actually subtract 137 – 49 which gives me 88 which is very close to my estimated answer of 90.
What if I just have a subtraction problem: 542 – 67. I could either do 54070 or 50070. Which one is easier but gives me a more accurate answer? 540 – 70. Would both be an estimation? Yes. But I also want my answer to be reasonable. If we actually solve 54267=475. When I solve both of my estimation problems, the one that gives me an answer closer to 475 is 54070. So if your ever stuck on which place to estimate to, you can always try both problems and then when you actually solve the problem, see which one is closer. When checking it may take you more time, but it can help you get a more reasonable answer. Eventually your brains will just automatically see which place is the most reasonable to round to. 
Guided Practice: 
Now let’s see if you can figure out the best estimate for these problems.
298 – 43
6,798 – 721
3,702 – 934
What is my first step? (To see what place makes the MOST sense to round to and that will give me a REASONABLE answer) What place should I round to? What would I round each number to? How would I set it up? What’s the answer? How could I check it?

Independent Practice: 
Students will complete a worksheet with 10 subtraction and bonus addition estimation word problems ranging from 1digit to 4digit numbers. 
Math Journal: 
Describe in your journal how you pick the places to round to when your estimating. Then tell me: Why is it important to check if your answer is reasonable? 
Closing: 
Today we reviewed that the purpose of estimation is to make adding and subtracting bigger numbers or a bunch of numbers easier by choosing the most reasonable place to round to that will make it easier for us as mathmeticians to solve. 
Center Options: 

Differentiation: 
Struggling students should stick with extra practice on front end rounding of whole numbers or can try estimating addition of 1digit numbers.
Advanced students should be given larger digit number to subtract with and when appropriate subtract with 3 numbers instead of 2, starting with the biggest number on top. 
Lesson Resources
Estimating Differences Powerpoint Smart Board 
684

Estimating Sums Diffs 
533
