Estimate Sums and Differences by Rounding

Examples, solutions, and videos to help Grade 3 students learn how to estimate sums and differences of measurements by rounding, and then solve mixed 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 21
Worksheets for Grade 3

Application Problem

Gloria fills water balloons with 238 mL of water. How many milliliters of water are in 2 water balloons? Estimate to the nearest 10 mL and 100 mL.
Which gives a closer estimate?

Note: This problem reviews Lesson 17 by having students round to estimate sums and then calculate the actual answer. It reviews addition because this lesson includes mixed practice with addition and subtraction.

Concept Development

Each table has the premeasured items and measurement tools listed below. Students work together to measure weight, length, and capacity.
Next, they round to estimate sums and differences, then use the standard algorithm to solve.

Materials Description (per table)
Problem 1: 1 digital scale, 1 bag of rice premeasured at 58 grams, 1 bag of beans premeasured at 91 grams
Problem 2: 1 meter stick, labeled Yarn A, B, and C (Yarn A premeasured at 64 cm, Yarn B premeasured at 88 cm, Yarn C premeasured at 38 cm)
Problem 3: 1 400-milliliter beaker, Container D premeasured at 212 mL, Container E premeasured at 238 mL, Container F premeasured at 195 mL
Problem 4: No additional materials

Homework

1. There are 153 milliliters of juice in 1 carton. A 3-pack of juice boxes contains a total of 459 milliliters.
   a. Estimate, and then find the total amount of juice in 1 carton and a 3-pack of juice boxes.
   153 mL + 459 mL ≈ ____ + ____ =____
   153 mL + 459 mL = ____
2. Mr. Williams owns gas stations. He sells 367 liters of gas in the morning, 300 liters of gas in the afternoon, and 219 liters of gas in the evening.
   a. Estimate, and then find the total amount of gas he sells in one day.
   b. Estimate, and then find the difference between the amount of gas Mr. Williams sells in the morning and the amount he sells in the evening.

Try the free Mathway calculator and problem solver below to practice various math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

We welcome your feedback, comments and questions about this site or page. Please submit your feedback or enquiries via our Feedback page.