This document provides lesson plans and materials for a lesson on estimating sums by rounding measurements to various places values (tens, hundreds, fifties) and applying these skills to solve multi-step word problems involving adding measurements. The lesson includes fluency practice with counting, a sprint rounding numbers to the nearest ten, worked examples of rounding and adding various measurement values, analysis of estimates compared to exact sums, and an application word problem asking students to estimate and find the precise total amount of medicine prescribed over two days.

1. Place Value and Problem Solving
with Units of Measure
Topic D: Two- and Three-Digit
Measurement Addition Using the Standard
Algorithm
Module 2: Lesson 17
Objective: Estimate sums by rounding and apply to
solve measurement word problems.

2. Fluency Practice
Group Counting (3 minutes)
We’re going to count forward and backward!
• Threes to 30
• Fours to 40
• Sixes to 60
• Sevens to 70
• Eights to 80
• Nines to 90
Make a connection to multiplication by tracking the
number of groups you count using your fingers!

3. Sprint (9 minutes)
• Complete the Round to the Nearest 10 sprint

4. Concept Development
(33 minutes)
Problem 1:
• What is 362 rounded to the nearest hundred?
• Let’s write it directly below 362.
• What is 159 rounded to the nearest hundred?
• Let’s write it directly below 159.
• What is 400 + 200?
• We estimated the sum by rounding to the nearest
hundred and got .
Now let’s estimate the sum by rounding to the nearest 10!
Estimate the sum of 362 + 159 by
rounding.

5. Concept Development
(33 minutes)
We’ve learned to round to the nearest ten and hundred before. Let’s think if
there is another way we could round these numbers that would make them
easy to add.
Let’s try rounding to the nearest 50…
What is 363 rounded to the nearest fifty?
What is 159 rounded to the nearest fifty?
What is 350 + 150?
We have three different estimated sums. Talk to your partner. Without
finding the actual sum, which estimate do you think will be closest?

6. Concept Development
(33 minutes)

7. Concept Development
(33 minutes)
Now let’s find the actual sum of 362 + 159
How did you predict which way of estimating would be closer?
We think about how to round in each situation to make our estimates as precise
as we need them to be.

8. Concept Development
(33 minutes)
Problem 2: Analyze the rounded sums of three expressions with addends
close to the halfway point: (A) 349 + 145, (B) 352 + 145, and (C) 352 + 151.
(Write the three expressions above on the board.) Take 90 seconds to find the
value of these expressions.
What do you notice about the sums 494, 497, and 503?
Analyze why the sums were so close by looking at the parts being added.
What do you notice?
Let’s round each number to the nearest hundred as we did earlier. (Lead the
students through rounding each addend as pictured below.) Talk to your
partner about what you notice.

9. Concept Development
(33 minutes)
A very small difference in the numbers can make a difference in the way
we round and also make a big difference in the result. How might you
get a better estimate when you see that the addends are close to
halfway between your rounding units?
Think about why 352 + 145 had the estimate closest to the precise
answer. Share with your partner.
Why do we want our estimated sum to be about right?
Would all three estimates help you to check if your exact answer is
reasonable, if it makes sense?
So we need a close estimate to see if our actual sum is reasonable.

10. Concept Development
(33 minutes)
Problem 3:
Round the sum of 296 + 609.
Analyze how rounding to the nearest hundred is nearly the same as rounding to the
nearest ten when both addends are close to a hundred.

11. The doctor prescribed 175 milliliters of medicine on Monday and 256
milliliters of medicine on Tuesday.
Estimate how much medicine he prescribed in both days.
Precisely how much medicine did he use in both days?
To solve Part (a), first determine how you are going to round your numbers.
Application Problem
(5 minutes)

13. Problem Set (10 minutes)
Student Debrief (10 minutes)
Exit Ticket (3 minutes)

14. Homework
3-2 Lesson 17
Homework
Is Due Tomorrow!