Year 8 Mathematics · AC9M8M04

Duration, 12/24-Hour Time and Time Zones

Treat a clock reading and an elapsed duration as different quantities. Convert moments to one common time-zone reference before comparing them, and track date changes…

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Key conceptTeach from the board

A clock time tells when an event occurs; a duration measures the interval between two moments. Displayed local times cannot usually be subtracted directly when locations have different UTC offsets.

A reliable method is: write each location’s offset, convert both moments to UTC (or another shared reference), compare them there, then convert back if the answer requires a local time. Crossing midnight may change the calendar date.

Preserve the AC9 elaborations: using digital tools to compare Perth with places such as Suva or Toronto, planning recurring virtual meetings across Australian jurisdictions with daylight-saving complications, and creating international travel itineraries across Asian time zones.

Worked examplesWe do

Worked examples

AC9M8M04 - Duration, 12/24-Hour Time and Time Zones
Example 1

Convert 6:48 am, 12:05 pm and 9:17 pm to 24-hour time.

Example 2

Find the duration from 18:55 to 22:30.

Example 3

Find the duration from 23:40 to 02:15 next day.

Example 4

Convert 10:00 at UTC+8 to UTC+12.

Curriculum examplesCopied content

Australian Curriculum v9.0 — AC9M8M04: solve problems involving duration, including using 12- and 24-hour time across multiple time zones.

Victorian Curriculum F–10 Version 2.0 — Level 8, VC2M8M04:Exact.

NSW Mathematics K–10 Syllabus (2022) — Stage 4, MA4-RAT-C-01; MAO-WM-01:Supporting. NSW Stage 4 has no clean one-outcome equivalent for the full national time-zone descriptor; rate/distance-time and Working mathematically support elapsed-time reasoning without pretending exact equivalence.

LessonAC v9VictoriaNSW
Duration/time zonesAC9M8M04VC2M8M04 — ExactMA4-RAT-C-01; MAO-WM-01 — Supporting
Questions and answersWith answers
  1. Why use 24-hour time? It removes am/pm ambiguity and is useful for schedules.
  2. Why convert to UTC? It provides one common reference for different zones.
  3. What can happen when an offset pushes time past 24:00? The calendar date changes.
  4. Why can a recurring meeting shift seasonally? Some locations change UTC offset for daylight saving while others do not.
Practice and reviewReady for practice
  • Subtracting local times directly. Convert to one common zone first.
  • Treating 12:00 am as noon. 12:00 am is midnight; 12:00 pm is noon.
  • Ignoring the date. Time-zone conversion or travel can cross into the previous/next day.
  • Assuming an Australian zone’s offset never changes. Daylight saving may change the offset in some jurisdictions and dates.
Curriculum alignmentStart here
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