Time

 Mind Maps

Class IV - maths: Time
One Word Answer Questions:
Q) What is the time now ?
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Q) Write the time in minutes past hour?
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Q) 4'oclock in the morning.Express the time in a.m or p.m?
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Q) What time is 2 hours after 6:05 a.m ?
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Q) What time is 3 hours before 9:05 p.m ?
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Q) In a leap year, February has ___ days.
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Q) 0000 is also written as _____ hours which means that the day is over
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Q) In 24 hour clock time 1:45p.m. is written as _____ hours
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Q) 1 hour after midninght=?
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Q) Convert 5 minutes into seconds?
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Q) 1 year= ________ weeks .
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Short Answer Questions:
Q) Convert 15 days in to hours ?
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Q) Convert 8 hours 25 minutes in to minutes ?
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Q) Convert 17 minutes 15 seconds into seconds?
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Q) Change time 9:30 a.m into 24-hour clock time ?
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Q) Add the units of time 8 hrs 12 mins;6 hrs 13 mins 45 secs and 4 hrs 40 mins 32 secs ?
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Q) Convert the 12 minutes into seconds ?
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Q) Convert 4 minutes 5 seconds into seconds
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Q) Subtract 5 hours 45 minutes from 8 hours 25 minutes?
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Q) Subtract 11 hrs 25 mins 30 seconds from 20 hours?
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Q) Convert 5 minutes 10 seconds into seconds ?
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Long Answer Questions:
Q) Subtract 8 hrs 24 mins 50 secs from 12 hrs 65 mins 60 secs ?
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Q) Sailaja went shopping at 11:00 a.m. and returned at 1:45 a.m. How long was she away ?
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Q) Madhu gose to school at 7:20 a.m. and returns at 3:30 p.m. How long is she away from home?
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Q) Meena's aunt was on a long visit of 54 daya to Dubai.If she reached there on 10 May, On what date would she be leaving?(include 10 May.)
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Q) Write the dates in short form (i)15 April 1994 (ii)14 May 2017 (iii)12 June 2004 (iv)5 oct 2016 (v)5 Aug 2006
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Q) Convert 12:30 pm to 24 hour clock time.
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Q) Add 10 hrs 35 minutes 25 seconds and 8 hrs 30 minutes 45 seconds.
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Q) Mr. Joseph went shopping at 11:15 a.m. and returned at 12:45 p.m. how long he was away?
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Q) Aman left home at 7:45 a.m. and reached his school at 9:00 a.m. how long did it take Aman to reach his school?
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Q) What time it will be 3 hours 20 minutes after 4:30 p.m.?
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Q) Convert 7 days into hours?
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Q) Mr.Mehra goes to office at 9:30 am and returns at 5:00 pm. How long is he away from home?
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Time

### Time

Definition
Time is an observed phenomenon by which human beings sense and record changes in the environment and in the universe.

Example: The above time is 2 O'clock. Analog Clock: A clock or watch which has moving hands and hours marked from 1 to 12 is called analog clock or watch.

Example: Digital Clock:A clock or watch in which hours, minutes and sometimes seconds are indicated by digits, rather than hands on a dial is called digital clock or watch.

Example: If we look at the digital clock, it is easy to read because it displays the exact time than the analog clock

Time to Exact Minute

In the above example, it is easy to read time from the digital clock but in the analog clock the minutes hand is yet to reach 11.

• If you look at the clock closely, you will find that between the numbers written on its face i.e., 1, 2, 3,..... there are smaller lines or dots which correspond to a single minute.
• So, between 1 and 2 there are 4 lines which divide the space between 1 and 2 into 5 equal parts.
• Similarly the space between 2 and 3 is also divided into 5 equal parts by 4 lines.
• In the figure below, you see that the minute hand is at 30 and the hour hand is in between 9 and 10. So, the time is 9 : 30.
• • Now, in clocks which you see, the numbering of minutes (up to 60) is not done. Then how do we read minutes?
• You know how to count the minutes in fives. When the minutes hand is at 7, it is 35 minutes past the hour and when the minute hand is at 8 it is 40 minutes past the hour.
• So, between 7 and 8 will lie the minutes 36, 37, 38, 39.
• If the minute hand is at the first line, it is 36 minutes past the hour.
• If it is at the second line, it is 37 minutes past the hour and so on.
A.M and P.M
• We divide the day into 24 hours, but on a clock we can see only 12 hours.
• In one day the hour goes round the face of the clock twice.
• When a clock shows 9 O'clock, is it 9 O'clock in the morning or it is 9 O'clock at night?
• In order to avoid such confusion, we use A.M. which means ante meridiem for the timings between 12 O'clock in the midnight and 12 O'clock at noon.
• We use P.M. which means post meridiem for the timings between 12 O'clock at noon and 12 O'clock midnight.
• So, 8 O'clock in the morning is 8 a.m. and 8 O'clock in the night is 8 p.m.
• For writing 12 O'clock, we do not use a.m. or p.m., we write 12 noon or 12 midnight. Example: What is the time?

1) One hour before 10 a.m.?
Answer = 9 a.m.
2) Three hours after 9 p.m.?
Answer = 12 midnight.
3) Two hours after 11 a.m.?
Answer = 1: 00 pm.
4) Four hours before 3 : 50?
Answer = 11 : 50

Seconds

Some clocks or watches have a third hand called the second hand. It is the thinnest and moves the fastest. It covers 60 small divisions in 1 minute.
It takes 1 second to move from one small division to the next.
Thus, 1 minute = 60 seconds.
Now, we are aware of three units of time i.e., hour, minute, and second.
Second is the smallest unit among the three, and hour is the largest.
1 hour = 60 minutes and
1 minute = 60 seconds. Conversion of Units of Time

Example 1: Convert 7 days into hours
Solution: We know that 1 day = 24 hours
So, 7 days = (7 × 24) hours = 168 hours.

Example 2: Convert 6 hours into minutes.
Solution: We know that 1 hour = 60 minutes
So, 6 hours = (6 × 60) minutes = 360 minutes.

Example 3: Convert 5 minutes into seconds.
Solution: We know that, 1 minute = 60 seconds
So, 5 minutes = (5 × 60) seconds = 300 seconds.

Example 4: Convert:

a) 7 hours 45 minutes into minutes
b) 4 minutes 5 seconds into seconds
Solution:

a) 7 hours 45 minutes = (7 × 60) minutes + 45 minutes
= 420 minutes + 45 minutes
= 465 minutes
b) 4 minutes 5 seconds = (4 × 60) seconds + 5 seconds
= 240 seconds + 5 seconds
= 245 seconds.

24 - Hour Clock Time

The 24-hour clock time is used by the Railways and the Airlines. Some offices also work by the 24-hour clock. • The 24 hour clock time does not use a.m. and p.m.
• Time begins from midnight which is indicated as 0000 hours.
• The first 2 zeros stand for hours and the next 2 zeros stand for minutes.
• 3 a.m. is written as 0300 hour.
• 1 p.m. is written as 1300 hours.
• 12 + 1 = 13 hours
• 1: 45 p.m. is written as 1345 hours.
• 4 p.m. is written as 1600 hours - 12 + 4 = 16 hours.
• 0000 is also written as 2400 hours which means that the day is over.
Addition and Subtraction of Time

While adding or subtracting in units of time, we write each unit under its particular heading.

Example 1: Add 6 hours 75 minutes and 4 hours 25 minutes.

• Write under the correct heading.
• Add the minutes.
75 mins + 25 mins = 100 mins = 60 mins + 40 mins
= 1 hr and 40 mins
• Write 40 in the minute's column and carry 1 hr to the hour's column.

• Add the hours.
6 hrs + 4 hrs + 1 hr (carried over) = 11 hrs
• Write 11 in the hour's column. Answer = 11 hours 40 minutes.

Example 2: Add 10 hrs 35 minutes 25 seconds and 8 hrs 30 minutes 45 seconds

• Write under the correct heading
• Add the seconds.
25 secs + 45 secs = 70 seconds
= 70 seconds
= 60 seconds + 10 seconds
= 1 minute and 10 seconds.
• Write 10 under the second's column and carry 1 to the minute's column

• Add the minutes.
35 minutes + 30 minutes + 1 minute (carried over)
= 66 minutes
= 60 minutes + 6 minutes
= 1 hour 6 minutes
• Write 6 in the minute's column and carry 1 to the hours column

• Add the hours.
10 hours + 8 hours + 1 hour (carried over)
19 hours
• Write 19 under the hours column. Answer = 19 hrs 6 mins 10 secs.

Example 3: Subtract 5 hours 45 minutes from 8 hours 25 minutes
Solution:

• Write the bigger number under the smaller number under the same unit columns.
• 45 minutes cannot be subtracted from 25 minutes
So, regroup hours into hours and minutes.
1 hr from the hour's column is taken to make 60 mins + 25 mins leaving 7 hours in the hour's column.
• Subtract the minutes
85 mins - 45 mins = 40.
• Subtract the hours
7 hours - 5 hours = 2 hours
• Answer = 2 hours 40 minutes.

Example 4: Subtract 11 hrs 25 mins 30 seconds from 20 hours.
Solution:

• Write under the same unit columns.
• There are no seconds and no minutes in the minuend. So, we need to regroup as shown.
• Subtract the seconds.
60 secs - 30 secs = 30 secs
• Subtract the mins.
59 mins - 25 mins = 34 mins
• Subtract the hours.
19 hrs - 11 hrs = 8 hrs.
• Answer = 8 hrs 34 mins 30 secs.

Time Duration
Calculating The Hours And Minutes Elapsed

If we know when an activity started and when it was over, we know the duration of the activity, i.e., how long it took or how much time elapsed
Example 1:Aman left home at 7:45 a.m. and reached his school at 9:00 a.m. how long did it take Aman to reach his school?
Solution:7:45 a.m. → 8:00 a.m. → 9:00 a.m.
15 minutes    1 hour
So, Aman takes 15 mins + 1 hour = 1 hour 15 minutes to reach his school.

Example 2: Mr.Mehra goes to office at 9:30 am and returns at 5:00 pm. How long is he away from home?
Solution: 9:30 a.m. → 10:00 a.m. → 5:00 p.m.
30 minutes     7 hours
So, Mr.Mehra is away for 7 hours 30 minutes.

Example 3: Mr. Joseph went shopping at 11:15 a.m. and returned at 12:45 p.m. how long he was away?
Solution: 11:45 a.m. → 12:00 p.m. → 12:45 p.m.
15 minutes    45 minutes
So, Mr. Joseph was away for 15 minutes + 45 minutes = 60 minutes = 1 hour

Example 4: What time it will be 3 hours 20 minutes after 4:30 p.m.?
Solution:3 hours after 4:30 p.m. is 7:30 p.m.
20 minutes after 7:30 p.m. is 7:50 p.m.

All the above examples states that if we know the starting time and the duration time of certain activity, we can find the finishing time.

Days In An Year

Let us look at the months in year and days in month.

• The months January, March, May, July, August, October, and December have 31 days each.
• The months April, June, September, and November have 30 days each.
• The month February has 28 days.
• Let us add these days.
• The number of days in April, June, September, and November have 30 days.
So, the total number of days in these 4 months = 30 × 4 = 120
• Number of days each in January, March, May, July, August, October, and December is 31.
So, total number of days in these 7 months = 31 × 7 = 217
• Number of days in February = 28
• Total number of days in 12 months = 120 + 217 + 28 = 365 days.
• So, the total number of days in one year(12 months) = 365.

But, if we notice the year 2008, it has 29 days.
When we talk about a year, it is actually the time taken by the Earth to go round the Sun once.
But the earth takes 365 1/4 days to do so.

Now, 1/4 + 1/4 +1/4 + 1/4 is the same as 1/4 × 4 = 1.
Though each year is taken to be 365 days, this extra day is added to the year every fourth year.
Then that year has 366 days.

Leap Year

In a leap year, February has 29 days.
How to remember the days in each month?
Use your knuckles!!!
All the knuckles show the months with 31 days.
The rest except February show 30 days. Calculating Number of Days

Let us calculate the number of days between two given dates.
Example 1:Sushant's school closed for summer vacation on 20 April and opened on 14 June. How many days of vacation did Sushant have?
Solution: This means Sushant did not go to school on 20 April, however he went on 14 June.
So, we need to include 20 April in the calculation.
But, we need to exclude 14 June from it.
April has 30 days. So, number of days of vacation in April = (30 - 19) = 11 days.
May has 31 days. So, number of days of vacation in May = 31 days.
Number of days of vacation in June = 13 days(because the school reopened on 14 June)
Total number of days of vacation = 11 + 31 + 13 = 55 days.
So, Sushant has 55 days of vacation.

Example 2: Mother takes 19 days leave from the office. If her last working day is 24 August, on what day does she have to join the office?
Solution: Mother was out on leave on the 24th, so it is not a part of 19 days of leave taken.
August has 31 days, so number of days of leave in August = 31 - 24 = 7 days.
Number of days of leave in September will be 19 - 7 = 12 days.
So, Mother has to join office on 13 September.

Example 3: How many dates are there from 5 January to 14 March, if it is not leap year? (Include both dates)
Solution:
Days in January = 31 -4 = 27 days
Days in February = 28 days
Days in March = 14 days
So, total number of days = 27 + 28 + 14 = 79 days.

Example 4: What day is the 21st day after 13 March?
Solution: Here, we do not include 13 March in the number of days.
Number of days in March = 31 - 13 = 18 days
Number of days in April = 21 - 18 = 3 days
So, the date is 3rd April.

Writing Date, Monthv Year in Short Form

We write 15 August 2012, as
15 08 2012
DAY MONTH YEAR
In short form, it is written as 15.08.2012.

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