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CBSE Class 4 · Mathematics

Ticking Clocks and Turning Calendar

Official NCERT chapter from Math-Mela (book code demm1). ExamMaster notes are original teaching at CBSE Class 4 depth.

This lesson follows the official chapter “Ticking Clocks and Turning Calendar” in Math-Mela. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 4
  • Easy level
  • 8 concepts

129 February exists only in a leap year

Most years, February has 28 days. In a leap year it has 29. 29 February is a date that appears only then.

Writing 29 February in a common year is a broken date.

Figure. 29 February is not on every calendar. Three common years end February at 28; the fourth, the leap year, earns the extra day. The date is a year-test, not a missing square on a clock.

How it works

  1. Ask leap or commonDoes this year have 29 Feb?
  2. If leap, 29 Feb is a real boxA date.
  3. If common, February ends on 28No 29.

2A birthday is a date on a turning calendar

A birthday is a month-and-day box that returns each year. The weekday can change; the date-name can stay.

“My birthday lasted three hours” mixes date with duration.

Figure. A birthday is one cell on a turning calendar, not a number floating free. The highlighted 12 is a date in a named month; next year the same name lands on a different weekday as the calendar turns.

How it works

  1. Name the month and dayThe box.
  2. Find it on this year’s calendarA cell.
  3. Keep duration out of the date-nameHow long the party lasts is later.

3Months and weeks still repeat

Twelve month-names, then January again. Seven weekday-names, then Monday again.

A thirteenth month is a miss. An eighth weekday is a miss.

Figure. Weeks do not invent new day-names. After Sunday the track starts again at Monday. Months keep their own lengths, but the 7-day cycle is the same strip reused.

How it works

  1. List the cycle you needMonths, or weekdays.
  2. See the last nameDecember, or Sunday.
  3. Say the nextJanuary, or Monday.

4A clock face is a turning track

The hands travel a circle. That circle is a track of 12 hour-marks and 60 minute-marks.

A stopped clock is not a turning track.

Figure. A clock face is a turning track. Opened out, the rim is this line of hour marks: 12, 3, 6, 9, and 12 again. The hand sits on a mark; it does not need a drawn circle to name the hour.

How it works

  1. See the circleThe face.
  2. See a hand moveAlong the track.
  3. Read where it pointsA mark on that track.

5Hour hand and minute hand name different units

The short hand names the hour. The long hand names the minutes. Swapping them misreads the clock.

Both can move; they still name different units.

Figure. The hour hand and the minute hand count the same turning, but they name different units. One hour is sixty minutes — two names for one span, not two lengths to add. Mixing the unit mid-count is how a duration becomes a nonsense number.

How it works

  1. Find the short handHour.
  2. Find the long handMinutes.
  3. Read each unitDo not swap.

6Duration is how long the party lasts

From 4 o’clock to 6 o’clock is 2 hours — a duration. 6 o’clock is a clock-time, not a duration.

Do not mix “what time” with “how long” in one unmarked sentence.

Figure. Duration is how many of the same hour-units fit between start and end. From 4 o'clock to 7 o'clock three hours fit. The 7 is the end mark, not the length.

How it works

  1. Mark start time4:00.
  2. Mark end time6:00.
  3. Count the span2 hours.

Party duration

A party starts at 4:00 and ends at 6:00. How long is it?

  • Start4:00
  • End6:00
  • Duration2 hours

Pro tip. Duration is the span. 6:00 is the end-time, not the length.

7Yesterday and tomorrow sit on the calendar

Yesterday is the box before today. Tomorrow is the box after. They are neighbours.

Yesterday is not a duration of many days.

Figure. Yesterday and tomorrow are the date cells on either side of today. They sit on the calendar line; they are not a feeling about time. Crossing midnight moves the highlight one cell right.

How it works

  1. Find today’s boxThe date you mean.
  2. Step one backYesterday.
  3. Step one forwardTomorrow.

8A missing 29 February is a year-test, not a broken clock

No 29 Feb means a common year, not a clock that skipped an hour. Date-holes and clock-hands are different tools.

Do not “fix” February by moving a clock hand.

Figure. A February that stops at 28 is a common year, not a broken clock. The extra 29 is the leap-year mark. Check the year first; do not look for a missing hour on the clock face.

How it works

  1. See a missing 29 FebYear-test: common year.
  2. Leave the clock out of itHands name hours.
  3. Use the calendar tableMonth lengths.
29 February appears
  1. Only in a leap year
  2. Every year
  3. When the clock skips an hour

A year-test, not a clock-test.

Notes

  • The official chapter title is “Ticking Clocks and Turning Calendar”. Teach the school test for that title, not a contest shortcut.
  • If a step needs a later class, stop. The next official chapter will pick it up.

Formulas

  • Leap year: February has 29 days. Common year: 28.
  • Duration = end time - start time (same day, hours you can count).
  • 7 weekday names, then the week repeats.

Reference tables

29 February is a leap-year box. A common year ends February on 28.

February’s last day
Kind of yearLast date in February
Common year28 February
Leap year29 February

Recap

Hold these pegs from the official chapter “Ticking Clocks and Turning Calendar”. The wording is ExamMaster’s teaching, not a textbook recap.

29 February exists only in a leap year
Most years, February has 28 days. In a leap year it has 29. 29 February is a date that appears only then.
A birthday is a date on a turning calendar
A birthday is a month-and-day box that returns each year.
Months and weeks still repeat
Twelve month-names, then January again. Seven weekday-names, then Monday again.
A clock face is a turning track
The hands travel a circle. That circle is a track of 12 hour-marks and 60 minute-marks.
Hour hand and minute hand name different units
The short hand names the hour. The long hand names the minutes. Swapping them misreads the clock.
Duration is how long the party lasts
From 4 o’clock to 6 o’clock is 2 hours — a duration.

Practise Ticking Clocks and Turning Calendar

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