Time — Class 4 Mathematics (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 4 Mathematics, Unit 5. Days and weeks, marking dates, days in a year, and reading clock time. Taught in August.

1. Days and weeks

A week has 7 days: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday.

Five of them are school days — Monday to Friday. Two are holidays — Saturday and Sunday.

The week never ends; it loops. After Saturday comes Sunday again, and the count starts over.

2. Reading a calendar

A calendar shows the days of the week arranged under the month, so you can find the date of any particular day.

Here is August 2023, the month the textbook uses:

Read down a column to find every date that falls on the same day. The Wednesdays are 2, 9, 16, 23 and 30. So the third Wednesday is the 16th.

Now try the trickier phrasing. "The day after the second Sunday": the Sundays are 6, 13, 20 and 27, so the second Sunday is the 13th and the day after is the 14th. "The day before the fourth Tuesday": the Tuesdays are 1, 8, 15, 22 and 29, so the fourth is the 22nd and the day before is the 21st.

3. Months and the days they hold

A year has 12 months and 365 days.

4. Weeks in a year

Since a week is 7 days, divide the days of the year by 7.

365 ÷ 7 = 52 remainder 1

So an ordinary year holds 52 weeks and 1 day.

5. Leap years

A leap year comes once every 4 years. February gains an extra day and holds 29 days, so the year has 366 days.

366 ÷ 7 = 52 remainder 2

A leap year is 52 weeks and 2 days.

6. Reading a clock

A clock face carries the numbers 1 to 12 and three hands:

• the short hand is the hour hand, and it moves slowest
• the long hand is the minute hand
• the thin, usually red hand is the second hand, and it moves fastest

One full circle of the minute hand is one hour, and 1 hour = 60 minutes.

Because 60 divides neatly into quarters, we have names for the useful positions:

Note the switch at the bottom of the hour. Up to the half hour we count past the hour just gone; after it we count to the hour coming.

7. The 24-hour clock

An ordinary clock shows 3 o'clock twice a day, so we add am for the morning half and pm for the afternoon and evening half. Railways cannot risk that confusion, so they number the hours straight through from 00 to 23. This is railway time.

To convert from a 12-hour time to a 24-hour time:

• Morning (am): the hour stays the same. 8:30 am becomes 08:30.
• Afternoon and evening (pm): add 12 to the hour. 2:30 pm becomes 14:30, and 9:15 pm becomes 21:15.

Two special cases are worth learning by heart, because they are the ones that catch people out:

• 12 noon stays 12:00. Do not turn it into 00:00.
• 12 midnight becomes 00:00.

A railway ticket printed 14:30 means half past two in the afternoon.

8. Finding how long something lasts

The duration is the gap between a start time and an end time. Subtract the start from the end, remembering that an hour is 60 minutes and not 100.

A programme runs from 9:15 am to 11:45 am. The hours give 11 − 9 = 2, and the minutes give 45 − 15 = 30. The duration is 2 hours 30 minutes.

When the end minutes are smaller than the start minutes, borrow an hour as 60 minutes. From 9:40 am to 11:20 am: borrow, so the minutes become 80 − 40 = 40 and the hours 10 − 9 = 1. The duration is 1 hour 40 minutes.

9. Worked examples

Example 1. Which is the third day of the week if the week starts on Sunday?

Solution: Sunday, Monday, Tuesday.

Example 2. Using the August 2023 calendar, what date is the second Saturday?

Solution: The Saturdays are 5, 12, 19 and 26. The second is the 12th.

Example 3. How many weeks and days are there in 30 days?

Solution: 30 ÷ 7 = 4 remainder 2, so 4 weeks and 2 days.

Example 4. February has 28 days. How many weeks is that exactly?

Solution: 28 ÷ 7 = 4 with no remainder, so exactly 4 weeks.

Example 5. Ravi reaches school at 8:30 am. Prabu arrives 30 minutes later. When does Prabu reach?

Solution: 8:30 + 30 minutes = 9:00 am.

Example 6. Write the missing month: June, ______, August, September.

Solution: July.

Example 7. True or false: March comes between September and November.

Solution: False. October comes between September and November.

10. Practice

1. How many days are there in a week, and how many of them are school days?
2. Using the August 2023 calendar, what is the date of the first Friday?
3. How many months have 31 days?
4. How many days are there in a leap year?
5. How many weeks and days make up an ordinary year?
6. Which hand of a clock moves fastest?
7. Write "quarter past 12" in numbers.
8. A film starts at 4:00 pm and runs for 30 minutes. When does it end?
9. Write the missing month: March, April, ______, ______.
10. Write 3:45 pm in 24-hour time.
11. Write 11:15 pm in 24-hour time.
12. What is 12:00 noon in 24-hour time?
13. How long is it from 9:15 am to 11:45 am?

11. Answers

1. 7 days, of which 5 are school days (Monday to Friday).
2. The 4th.
3. Seven months: January, March, May, July, August, October and December.
4. 366 days.
5. 52 weeks and 1 day.
6. The second hand.
7. 12:15.
8. 4:30 pm.
9. May, June.
10. 15:45 — add 12 to the hour.
11. 23:15.
12. 12:00. Only midnight becomes 00:00.
13. 2 hours 30 minutes.

12. Summary

• A week has 7 days: 5 school days and 2 holidays.
• Read a calendar down its columns to find every date falling on the same weekday.
• A year has 12 months and 365 days; seven months have 31 days, four have 30 and February has 28.
• 365 days is 52 weeks and 1 day.
• A leap year comes once in 4 years, has 366 days and 52 weeks and 2 days, and February gains a 29th day.
• The short hand shows hours, the long hand shows minutes, and 1 hour = 60 minutes.
• Quarter past is :15, half past is :30, and quarter to is :45 of the previous hour.