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 4 chapters and video availability01 · Read and understand
What you will learn
- Locate a first shared positive multiple.
- Explain your method and check what the result means in the stated situation.
Before you start
Multiplication and division facts, simple fractions, place value, and basic length and area measurement.
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
One classroom light blinks every 4 seconds and another every 6 seconds. They blink together at time zero. When next together?
Why this math matters
Use multiples to align repeating classroom schedules in a simplified timing model. 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.
Find when repeating schedules meet
PausedQuestion: Start with the question. Paused.
Question
Start with the question
One classroom light blinks every 4 seconds and another every 6 seconds. They blink together at time zero. When next together?
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
Four-second times: 4, 8, 12
List positive multiples of four.
Connect the parts
Six-second times: 6, 12
List positive multiples of six.
State and check the result
Next meeting: 12 seconds
Twelve is the smallest positive time in both lists.
The result
Next meeting: 12 seconds
Twelve is the smallest positive time in both lists.
Common mistakes to catch
- A shared multiple differs from a shared factor.
- State the common starting point and constant periods.
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
Two patterns repeat every 3 and 5 steps. What is their first shared positive step?
Show a hint
List small multiples.
Reveal answer and explanation
15
Fifteen is divisible by both three and five.
Practice 2
Why is time zero not the answer to 'when next'?
Show a hint
The initial meeting already happened.
Reveal answer and explanation
Next requires a positive time
Including zero would repeat the starting event rather than find a later one.
Take the idea with you
Use multiples to align repeating classroom schedules in a simplified timing model.
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: Classify numbers by their factors
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