 # Estimate Differences by Rounding

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Lesson Plans and Worksheets for Grade 3
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Examples, solutions, and videos to help Grade 3 students learn how to estimate differences by rounding and apply to solve measurement word problems.

Common Core Standards: 3.NBT.2, 3.NBT.1, 3.MD.1, 3.MD.2

### New York State Common Core Math Grade 3, Module 2, Lesson 20

Application Problem

Millie’s fish tank holds 403 liters of water. She empties out 185 liters of water to clean the tank. How many liters of water are left in the tank?

a. Estimate how many liters are left in the tank by rounding.

b. Estimate how many liters are left in the tank by rounding in a different way.

c. How many liters of water are actually left in the tank?

Concept Development

Problem 1:
Estimate 362 – 189 by rounding.

Problem 2
Analyze the estimated differences of four expressions with subtrahends close to the halfway point:
(A) 349 – 154, (B) 349 – 149, (C) 351 – 154, and (D) 351 – 149.

Problem 3
Round the difference of 496 – 209. Analyze how rounding to the nearest hundred is nearly the same as rounding to the nearest ten when both addends are close to 1 hundred.

Homework

2. Amy measures ribbon. She measures a total of 393 centimeters of ribbon and cuts it into 2 pieces. The first piece is 184 centimeters long. How long is the second piece of ribbon?
a. Estimate the length of the second piece of ribbon by rounding in two different ways.
b. Precisely how long is the second piece of ribbon? Explain why one estimate was closer.

3. The weight of a chicken leg, steak, and ham are shown to the right. The chicken and the steak together weigh 341 grams. How much does the ham weigh?
a. Estimate the weight of the ham by rounding.
b. How much does the ham actually weigh?

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