Learn with Amar
Teaching video
A teaching recording for this chapter has not been published yet. Start with the worked example below and explore the related animations where available.
Grade 2 chapters and video availability01 · Read and understand
What you will learn
- Keep a sum unchanged while moving an amount between addends.
- Explain your method and check what the result means in the stated situation.
Before you start
Counting and comparing whole numbers, basic addition and subtraction, and recognizing simple shapes.
Keep paper nearby. Read the question once for the context, then again to identify what is known and what you need to find.
Start with a question
Find 29 + 16 mentally.
Why this math matters
Move a small amount between groups to make a full ten before combining them. The worked example shows how to connect the situation, its mathematical representation, and a check on the result.
Set up the model
A useful answer starts with clear assumptions:
- Use the units, grouping rules, and reference whole stated in the question.
- Treat the supplied counts and measurements as exact within the classroom model, unless an estimate or a random outcome is requested.
02 · Work through the example
Follow the reasoning, one step at a time.
Try to predict the next step before reading it. After each calculation, explain why the operation makes sense and how it helps answer the original question.
Work through it with Amar
See this example unfold.
The complete worked example, one idea at a time.
Make an easier sum by moving one
PausedQuestion: Start with the question. Paused.
Question
Start with the question
Find 29 + 16 mentally.
Before you calculate
Read what is known and what you need to find. Make a prediction before moving to the first calculation.
Starts paused. Play advances through the full text at a reading pace; pause whenever you need more time. Previous, Next, and the phase buttons let you set your own pace. Playback pauses when this walkthrough leaves the screen or you switch tabs.
Your device’s reduced-motion setting keeps each phase still. Manual controls remain available. The full written solution stays below.
Represent the situation
29 needs 1 to make 30
A nearby full ten is easier to add.
Connect the parts
16 = 1 + 15
Move one from the second group to the first.
State and check the result
29 + 16 = 30 + 15 = 45
Moving an item between groups does not change their combined count.
The result
29 + 16 = 30 + 15 = 45
Moving an item between groups does not change their combined count.
Common mistakes to catch
- Balance any increase with an equal decrease.
- Compensation in a sum differs from changing only one addend.
03 · Practice independently
Try it before revealing the answer.
Use paper or a calculator as needed. Write your units and reasoning, then open the hint or explanation to check your approach.
Practice 1
Use compensation for 39 + 24.
Show a hint
Move one to thirty-nine.
Reveal answer and explanation
63
40 + 23 = 63.
Practice 2
Does changing 29 + 16 to 30 + 16 preserve the total?
Show a hint
Did you remove the added one elsewhere?
Reveal answer and explanation
No; it increases the total by 1
Compensation needs equal and opposite changes to the addends.
Take the idea with you
Move a small amount between groups to make a full ten before combining them.
04 · Reflect and continue
Can you explain it in your own words?
Before moving on, explain the main idea without looking at the worked example. Try both practice questions, check your reasoning, and name one mistake you now know how to avoid. Return to a step if you still need support.
Up next: Estimate with the nearest ten
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