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 5 chapters and video availability01 · Read and understand
What you will learn
- Use fractional units to justify decimal multiplication.
- Explain your method and check what the result means in the stated situation.
Before you start
Multi-digit operations, equivalent fractions, decimal place value, and rectangular area.
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
A rectangle measures 1.2 m by 0.4 m. What area?
Why this math matters
Use an area grid to see why products of tenths are hundredths. 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.
Multiply two decimal measurements
PausedQuestion: Start with the question. Paused.
Question
Start with the question
A rectangle measures 1.2 m by 0.4 m. What area?
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
1.2 = 12/10; 0.4 = 4/10
Both inputs are counts of tenths.
Connect the parts
(12 × 4)/(10 × 10) = 48/100
A tenth times a tenth produces a hundredth.
State and check the result
Area = 0.48 m²
The area is less than 1.2 m² because the width is less than one metre.
The result
Area = 0.48 m²
The area is less than 1.2 m² because the width is less than one metre.
Common mistakes to catch
- Multiplying two positive decimals below one makes a still smaller product.
- The place-value count comes from units, not guesswork.
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
Find 0.3 × 0.7.
Show a hint
Multiply three tenths by seven tenths.
Reveal answer and explanation
0.21
21/100 = 0.21.
Practice 2
Why does 2.5 × 0.2 equal 0.5 rather than 5?
Show a hint
One fifth of two and a half is half.
Reveal answer and explanation
The multiplier is two tenths
25/10 × 2/10 = 50/100 = 0.5.
Take the idea with you
Use an area grid to see why products of tenths are hundredths.
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: Share a decimal quantity equally
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