Year 5 Mathematics · AC9M5M03

Compare 12- and 24-hour time systems and solve practical problems involving the conversion between them

Students convert times around noon and midnight, read schedules and calculate elapsed time using timelines while distinguishing a clock time from a duration

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Learning goalsSay it simply

Students convert times around noon and midnight, read schedules and calculate elapsed time using timelines while distinguishing a clock time from a duration.

In 24-hour time, hours after noon continue 13–23; midnight begins 00:00 and noon is 12:00.

For pm times after 12:59, add 12 to the hour. For 13:00–23:59, subtract 12 and label pm.

Do not subtract time digits as ordinary decimals. Bridge through whole hours and check whether the interval crosses noon or midnight.

Learning routine: Represent → Reason → Calculate → Interpret → Verify

Success looks like

  • Represent accurately
  • Explain the relationship
  • Choose a suitable method or unit
  • Apply in context
  • Check and justify
Key conceptTeach from the board

Convert between 12-hour and 24-hour notation

12-hour24-hour12:00 am00:007:05 am07:0512:00 pm12:003:40 pm15:4011:59 pm23:59

For pm times after 12:59, add 12 to the hour. For 13:00–23:59, subtract 12 and label pm.

  1. Read every label and identify the quantities, parts or evidence.
  2. Explain the relationship shown—not just the final answer.
  3. Check the conclusion against the original question and units.

Use timelines for schedule duration

depart 14:35→to 15:00: +25 min→to 17:00: +2 h→arrive 17:18: +18 min→duration 2 h 43 min

Do not subtract time digits as ordinary decimals. Bridge through whole hours and check whether the interval crosses noon or midnight.

Now transfer the same relationship to a new situation and justify the result with precise vocabulary.

Clean visual examplesOne-page board

Clean one-page examples

AC9M5M03 - Compare 12- and 24-hour time systems and solve practical problems involving the conversion between them
Example 1

12-hour 24-hour 12:00 am 00:00 7:05 am 07:05 12:00 pm 12:00 3:40 pm 15:40 11:59 pm 23:59

Example 2

depart 14:35 → to 15:00: +25 min → to 17:00: +2 h → arrive 17:18: +18 min → duration 2 h 43 min

Example 3

12-hour 24-hour 12:00 am 00:00 7:05 am 07:05 12:00 pm 12:00 3:40 pm 15:40 11:59 pm 23:59

Example 4

depart 14:35 → to 15:00: +25 min → to 17:00: +2 h → arrive 17:18: +18 min → duration 2 h 43 min

Curriculum examplesCopied content

Content description: compare 12- and 24-hour time systems and solve practical problems involving the conversion between them.

  • E1: using timetables written in 24-hour time, such as flight schedules, to plan an overseas or interstate trip, converting between 24- and 12-hour time
  • E2: converting between the digital and analog representation of 24-hour time, matching the same times represented in both systems; setting the time on an analog watch using a digital alarm clock
Questions and answersWith answers

Core idea: In 24-hour time, hours after noon continue 13–23; midnight begins 00:00 and noon is 12:00.

Remember

  • Represent accurately
  • Explain the relationship
  • Choose a suitable method or unit
  • Apply in context
  • Check and justify

Important questions

  • Convert 3:40 pm. Explain using the model or evidence above.
  • Convert 00:25. Explain using the model or evidence above.
  • Explain noon and midnight. Explain using the model or evidence above.
  • Find 14:35 to 17:18. Explain using the model or evidence above.
  • Read a timetable. Explain using the model or evidence above.
Practice and reviewReady for practice
  • 12 am and 12 pm reversed — 12 am is midnight; 12 pm is noon.
  • Add 12 to every pm hour — Do not add 12 to 12 pm.
  • Minutes treated as hundredths — An hour has 60 minutes.
  • Leading zero omitted in formal 24-hour time — Write 07:05 for schedule clarity.

Learn from the Topic Guide and fixed Teacher Slides, complete the Practice Sheet, use Practice for supported feedback, then take the Test when ready.

Curriculum alignmentStart here

Students convert times around noon and midnight, read schedules and calculate elapsed time using timelines while distinguishing a clock time from a duration.

In 24-hour time, hours after noon continue 13–23; midnight begins 00:00 and noon is 12:00.

For pm times after 12:59, add 12 to the hour. For 13:00–23:59, subtract 12 and label pm.

Do not subtract time digits as ordinary decimals. Bridge through whole hours and check whether the interval crosses noon or midnight.

Learning routine: Represent → Reason → Calculate → Interpret → Verify

Success looks like

  • Represent accurately
  • Explain the relationship
  • Choose a suitable method or unit
  • Apply in context
  • Check and justify
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