Time
YEAR 8 GATS
TERM 2 WEEK 9
Converting Units of Time
Examples
Convert the following.
1. 3 h and 15 min to min.
E.g. Convert 3.7 hours to hours and minutes
Press: 3.7 = then the bubble button
2. 10 080 min to days.
3. 501 min to hours and
minutes.
Press the
bubble
button
3.7 h = 3 h 42 min
Cambridge textbook
EXERCISE 3J
Q1-(all),
Q’s2,4,5 - (every 2nd
part)
This is a link to a great video showing you how to use the Casio calculator to perform
time calculations
https://www.transum.org/software/SW/YouTube/Video.asp?
Movie=rDX93WuCCUw
24-Hour Time
The time of day is written in the 24-hour notation in the form hh:mm
(hours:minutes).
The day begins at midnight (00:00) and the last minute of the day begins at
23:59.
The advantage of the 24-hour clock is that it clearly distinguishes the time in
the morning and the afternoon without the a.m. and p.m. notation.
The 24-hour notation is used in many applications such as timetables, oven
clocks and airport arrivals and departures.
Examples:
a) Convert 8:15 p.m. to 24 hour
time.
b) Write 21:45 in 12 hour time.
Cambridge
textbook
EXERCISE 3J
Q6
Addition and Subtraction of Time
Algorithms (calculating without a calculator)
– If you would like to refresh this skill, please watch the video using the link
below.
https://www.youtube.com/watch?v=0nPuCgkc77E
Using the “bubble button” on Calculator
your calculator steps in red
1. 4 h 38 min + 7 h 44 2. How many hours and
min minutes from: b) 8.52am to 2.16pm
= 4°38° + 7°44° a) 3.46pm to 11.27pm [one am and one pm →change to 24h
= 12° 22° = 11°27° - 3°46° time]
= 12 h 22 min = 7° 41° = 14°16° - 8°52°
= 7 h 41 min = 5° 24°
= 5 h 24 min
Cambridge
textbook
EXERCISE 3J
Q3, 8, 14, 15,
Time Zones
Time zones have the same time irrespective of time differences.
Positive time zone number ‒ ahead GMT or UTC
Negative time zone number ‒ behind GMT or UTC
Australia has three time zones called the Eastern Standard Time
(+10), Central Standard Time (+9.5) and Western Standard Time
(+8).
• The Earth is divided into 24 time zones (one
for each hour).
• Twenty-four 15° lines of longitude divide the
Earth into its time zones. [15°=1hour,
1°=4minutes]
• Time zones also depend on a country’s
borders and its proximity to other countries.
• Time is based on the time in a place called
Greenwich, United Kingdom, and this is
called Coordinated Universal Time (UTC) or
Greenwich Mean Time (GMT).
• Places east of Greenwich are ahead in time.
• Places west of Greenwich are behind in time.
• Australia has three time zones:
Eastern Standard Time (EST), which is UTC
plus 10 hours.
Central Standard Time (CST), which is UTC
plus 9.5 hours.
Western Standard Time (WST), which is
UTC plus 8 hours.
Time differences
To calculate the local time.
1. Place the locations on an east west time line.
2. Find the time difference between the two locations.
3. Find the local time by adding or subtracting the time difference.
East of location – Add the time difference.
West of location– Subtract the time difference.
Examples
1. The time in Greenwich on the prime meridian is 1.00 p.m.
What is the standard time in Sydney (+10)?
Greenwi Sydney
ch
1.00pm
0 +10 +10
h
2. What is the standard time in New York (−5) when it is
9.00 a.m. in Sydney?
Sydney
New York
9,00am
-5 0 +10
-
15h
3. Sydney (GMT +10) and Port Pirie (GMT +9.5) .
a. What is the time difference between these places?
Port Pirie Sydney
Time difference = 0.5 hour or 30
+9.5 0.5 +10 minutes
h
b. What is the time in Sydney if it is 1.00 pm in Port Pirie
1.00p
m
Time in Sydney = 1.00pm + 0.5
+0.5 hour
h = 1.30pm
c. What is the time in Port Pirie if it is 10.00 am in Sydney?
10.00am
Time in Port Pirie = 1.00pm - 0.5
hour
-
= 12.30pm
0.5h
4. New York’s time zone is UTC (–5) and Tokyo is UTC (+9).
What is the local time in New York if it is 2.00 pm in Tokyo?
2.00p
New m
Tokyo
York
-5 0 +9
-
14h Cambridge textbook
EXERCISE 3J
Time in New York = 2.00pm - 14 Q9[choose 3],
hour 10[choose 3], 11, 15,
= 12.00am
18 to 21, 25.
