12
1. Revision on Time
Description


Recall conversion
of 12-hour clock
time to 24-hour
clock time and
vice versa.
Recall number of
days, weeks,
months, ordinary
years and leap
years.
Reflect and Review

To convert 6:45 p.m. to
24-hour clock time:
We add 12 hour to the
given time, i.e.,
6:45 hours + 12 hours
= 18:45 hours

Teasers
th
1) If 12 May in a
particular year is
Wednesday, on
which day will 7th
August fall in the
same year?
Answers
1) Saturday
2) 6:49
p.m.
2) Convert 18:49
hours into 12-hour
To find the number of leap
clock time.
years between 1990 and
2005:
Between 1990 and 2005,
1992, 1996, 2000 and
2004 are the only years
which are divisible by 4.
So, these are the 4 leap
years.
2. Converting Days into Hours
Description
Conversion of Days into
Hours:
To convert days into
hours, we have to
multiply the number of
days by 24.
Reflect and Review
Teasers
Answers
To convert 4 days into
hours:
1) Convert 56 days 14
hours into hours.
1) 1358
hours
4 days = 45 × 24 hours
= 1080 hours
2) Time taken by
Sameer to travel
from Delhi to
Hyderabad by train
is 1 day 18 hours.
Express the time
taken to travel in
hours.
2) 42
hours
1
3. Converting Hours into Minutes
Description
Reflect and Review
Conversion of Hours
into Minutes:
To convert hours into
minutes, we have to
multiply the number
of hours by 60.
To convert 7 hours 37 minutes
into minutes:
7 hours 37 minutes
= 7 × 60 minutes + 37 minutes
= 457 minutes
4. Converting Minutes into Seconds
Description
Reflect and Review
Conversion of
Minutes into
Seconds:
To convert minutes
into seconds, we
have to multiply the
number of minutes
by 60.
To convert 45 minutes 17
seconds into seconds:
45 minutes 17 seconds
= 45 × 60 seconds + 17 seconds
= 2717 seconds
5. Converting Hours into Days
Description
Reflect and Review
Conversion of Hours
into Days:
To convert hours
into days, divide the
number of hours by
24.
2
To convert 456 hours into days:
456 hours =
days = 19 days
Teasers
Answers
1) Convert 18 hours
21 minutes into
minutes.
1) 1101
minutes
2) Time taken by
Sumit to make his
science model for
the exhibition is 4
hours and 17
minutes. Express
the time taken in
minutes.
2) 257
minutes
Teasers
Answers
1) Convert 122
minutes into
seconds
1) 7320
seconds
2) Rahul spent 48
minutes in
gardening today.
Express the time
taken in seconds.
2) 2880
seconds
Teasers
Answers
1) Convert 3600
hours into days.
1) 150
days
2) Convert 5604
hours into days
and hours.
2) 233
days 12
hours
6. Converting Minutes into Hours
Description
Conversion of
Minutes into Hours:
To convert minutes
into hours, divide
the number of
minutes by 60.
Reflect and Review
To convert 563 minutes into hours
563 minutes =
hours
= 9 hours + 23 minutes
= 9 hours 23 minutes
Teasers
Answers
1) Convert 1880
minutes hours
and minutes.
1) 31
hours
20
minutes
2) Time taken by
Haris to walk
from school to
home is 95
minutes.
Express the
time taken in
hours and
minutes.
2) 1 hour
35
minutes
7. Converting Seconds into Minutes
Description
Reflect and Review
Teasers
Answers
Conversion of Seconds To convert 1440 seconds 1) Convert 2309
1) 38
into Minutes:
into minutes:
seconds into
minute
minutes
29
To convert seconds into 1440 seconds
seconds
minutes,
divide
the
=
minutes
number of seconds by 60.
2) Time taken by a
2) 2
= 24 minutes
train to cross a
minutes
level-crossing is 167
47
seconds. Express the
seconds
time taken in
minutes and
seconds.
3
8. Finding duration of time
Description
Reflect and Review
When we have to find
the duration of time:
Calculating the number of
Hours

To calculate the number of
hours from 9 a.m. of
Wednesday to 4 p.m. of
Friday:

Hours are added
to hours
Minutes are
added to minutes

Seconds are
added to seconds

Days are added to
days
From 9 a.m. of Wednesday
to 9 a.m. of Friday, it is 3
days, i.e. 24 x 3 = 72 hours.
From 9 a.m. of Friday to 4
p.m. of the same day, it is
7 hours.
Teasers
Answers
1) Ankit started cycling to
school from his village
at 7:35 a.m., and
reached school at 8:50
a.m. Find the duration
of time taken by him to
reach the collage.
1) 1 hour
15
minute
2) 12:29
p.m.
2) Swaroopa started
cooking at 10:12 a.m.
and took 2 hours 17
minutes to complete it.
At what time did she
complete cooking?
∴ Number of hours
= (72 + 7) hours = 79 hours.
Calculating the number of
Days
To find the duration in
number of days, if
Ankush’s annual
examinations started on
12th February 2015 and
ended on 4th March 2015:
1) The coaching classes
for a competitive exam
lasted for 51 days. If
the classes started on
11th of April, then when
did it end?
2) Siddharth was allotted
with a new project on
24 March 2014, which
th
got completed by 15
From 12 February 2015 to
th
January 2015. How
4 March 2015, we have
many days did
17 days in February and 4
Siddharth take to
days in March.
complete the project?
∴ Number of days
= (17 + 4) days = 21 days.
4
1) 1st June
2) 298
days
9. Temperature
Description

Temperature measures the
amount of heat (how hot or
cold something is).

Thermometer is used to
measure temperature.

The basic unit of
measurement is degree and
the standard unit is Celsius
scale (also called Centigrade
scale).



The Celsius scale is marked
from 0° to 100°. 0°C is the
freezing point of water and
100°C is the boiling point of
water.
Another scale for measuring
temperature is the
Fahrenheit scale. In this
scale, freezing point of water
is 32°F and boiling point of
water is 212°F.
Comparing the two scales we
have,
0°C = 32°F and 100°C = 212°F.
Reflect and Review
Teasers
Convert the
Conversion of Celsius
Scale to Fahrenheit Scale following
temperatures
To convert a temperature into Fahrenheit
scale.
from Celsius scale to
1) 780C
Fahrenheit scale, first
2) 500C
multiply the temperature
by and then add 32 to
it.
i.e., 0F = (
Answers
1) 172.40F
2) 1220F
) + 32
For example,
470C = (
) + 32
0
= 84.6 F
= 116.60F
Convert the
following
temperatures
into Celsius
To convert a temperature scale.
1) 1400F
from Fahrenheit scale to
2) 2500F
Celsius scale, first
subtract 32 from the
temperature and then
multiply it by .
Conversion of
Fahrenheit Scale to
Celsius Scale
i.e., 0C = (
1) 600C
2) 121.10C
)
For example,
950F = (95 – 32)
= 63
= 350C
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