Choose your route
Calculate unfamiliar sums and differences, including everyday situations.
Explore this lesson →16 practice questions · Optional read aloud · Thinking pad
Let’s understand the idea.
- Choose a way to calculate accurately. Written methods keep track of place values; other useful strategies split a number or use a nearby round number.
- Every exchange keeps the same value. To keep a sum, move an amount from one addend to the other. To keep a difference, shift both numbers by the same amount.
- Check the original question with the inverse operation. An estimate can flag an unreasonable answer, but an exact check is stronger evidence.
Something to notice
Ask the student to solve unfamiliar additions and subtractions independently on different days and explain one written step. Several valid methods are welcome. The API checks the numerical or selected reasoning answer; it does not automatically grade free-written work or establish fluent calculation from one untimed bank.
Try it. Change it. Explain it.
Open the lesson to use its pictures and controls. In How it works, connect the picture to the idea. In Play & discover, change the quantities and notice what stays the same. In Your turn, answer questions and use the explanation to check your reasoning.
You can ask for help, draw on the thinking pad, or listen to the question and answer options. Progress distinguishes independent work from work completed with help.
Let’s try it →Curriculum connection
Grade 3 · 3.NBT · US Common Core
This lesson is mapped to these standards. A completed activity is practice evidence, not a claim of mastery. Content is checked against the linked official standards and its mathematical models are tested.