Decompose Twice to Subtract

Examples, videos, and solutions to help Grade 3 students learn how to decompose twice to subtract measurements including three-digit minuends with zeros in the tens and ones places.

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 19

Download Worksheet for Common Core Grade 3, Module 2, Lesson 19

Application Problem

Jolene brings an apple and an orange with her to school. The weight of both pieces of fruit together is 417 grams. The apple weighs 223 grams.
What is the weight of Jolene’s orange?

Note: This problem reviews unbundling once to subtract. It also provides context leading into the Concept Development.

Concept Development

In the Application Problem, Jolene’s apple weighs 223 grams and her orange weighs 194 grams. (Draw the tape diagrams)
What should the question mark in the tape diagrams represent?
How much heavier the apple is than the orange?
How much more the apple weighs, in grams?
What equation can you use to find out how much heavier the apple is than the orange?
223 grams – 194 grams.
To subtract we need to decompose twice.
How much heavier is the apple than the orange?
The apple is 29 grams heavier than the orange!

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Homework

1. Solve the subtraction problems below.
   c. 423 cm - 136 cm
   e. 900 g - 58 g
2. The total weight of a giraffe and her calf is 904 kilograms. How much does the calf weigh? Use a tape diagram to model your thinking.
3. The Erie Canal runs 584 kilometers from Albany to Buffalo. Salvador travels on the canal from Albany. He must travel 396 kilometers more before he reaches Buffalo. How many kilometers has he traveled so far?
4. Mr. Nguyen fills two inflatable pools. The kiddie pool holds 185 liters of water. The larger pool holds 600 liters of water. How much more water does the larger pool hold than the kiddie pool?

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