TIME, CALENDAR AND DATE

Back to: Mathematics Primary 4

HELLO, WELCOME BACK TO CLASS

 

Time is the measured period during which an action, event or condition occurs. It can be measured using any of the following units; SECONDS, MINUTES, HOURS, DAYS, WEEKS, MONTHS AND YEARS. The standard unit for measuring time is SECONDS.

TABLE OF TIME

 

60 seconds	1 minutes (min)
60 minutes	1 hour (hr.)
24 hours	1 day (d)
7 days	1 week (wk.)
4 weeks	1 month
12 months	1 year (yr.)
365 days	1 year
366 days	1 leap year
10 years	1 decade
100 years	1 century
1000 years	1 millennium

 

 

CHANGING UNITS

When changing unit in time, the relationship between each unit as shown in the table of time above must be used.

 

Example:

 

• Mary recorded music for 145 minutes. How many hours and minutes did she record the music?

 

Solution 60minutes = 1 hour

 

This means when changing from minutes to hours, we divide by 60

• ¹⁴⁵₆₀

 

• 2 remainder 25

So therefore 145minutes = 2hrs 25minutes or 2 ²⁵₆₀ = 2 ₁₂⁵ hrs

 

• John worked on his mathematics homework for hours. How many minutes did he work for?

 

Solution

 

60 minutes = 1hour

 

This means when changing from hours to minutes, we multiply by 60.

2 ¹₂ = 2 ¹₂ × 60 minutes

• ⁵₂ × 60 = ³⁰⁰₂ = 150 minutes

 

 

• It took Moses exactly 3hours 17minutes to drive from Jos to Abuja. How many minutes is this?

 

Solution

3 hours = 3 × 60

 

= 180 minutes

 

3 hours 17minutes = 180 minutes + 17 minutes = 197 minutes

• The School Coordinator of Berkley Academy was on vacation for 2 weeks 4 days. How many days is this?

Solution

7 days = 1 week

This means that when changing days to week, we divide by 7 and when changing weeks to days, we multiply by 7.

2 weeks = 2 × 7 days = 14 days

2 weeks 4days = 14 days + 4 days = 18days

ADDITON AND SUBTRACTION OF TIME

Addition and subtraction can be done on time when the 12 hour clock and 24 clocks are well understood. Take a look at the table below:

 

12 hour clock	24 hours clock
7:00 am	7hrs 00min
4:30pm	16hrs 30mins
3:50am	3hrs 50mins
7:20pm	19hrs 20mins
12pm	12hrs 00min
12am	24hrs 00min

 

FROM A.M TO P.M change only p.m to 24 hour clock by adding 12 to it.

FROM P.M TO A.M change only a.m to 24 hour clock by adding 12 to it.

Example:

Susan worked at the hospital for 3 hours 35mins in the morning and 2hours 45minns. In the afternoon. How long did Susan work that day?

 

Solution:

5hrs 80mins can be further simplified because 80min is already more than 60 minutes.

80minutes = 1hr 20minutes

So therefore 5hrs 80mins = 5hrs + 1hr 20mins = 6hrs 20mins.

 

 

3.

 

is

19hrs 38mins 72seconds can be further simplified because 72seconds already more than 60seconds.

72 seconds = 1min 12secs

So therefore 19hrs 38mins 72seconds = 19hrs + 38mins + 1min 12seconds = 19hrs. 39mins 12seconds

• Joshua completed a job in 4hrs 30minutes. His sister Josephine completed the same job in 5hrs 15mins. How much longer did it take Josephine to finish the job?

Solution

STEPS TAKEN

• 30 minutes cannot be subtracted from 15 minutes so we have to borrow 1hr from 5hrs.
• hr borrowed from 5hrs is added as 60min since 1hr = 60minutes

• Afterwards, subtract normally.

 

STEPS TAKEN

^➢         48 seconds cannot be

subtracted from 32 seconds so we borrow 1min from 18mins which is added as 60 seconds to get 92 seconds because 1min = 60 seconds

• 18 minutes cannot be subtracted from the remaining 17 minutes so we borrow 1hr from 5hrs which is added as 60 minutes to get 77 minutes because 1hr = 60 minutes

• Final answer is 1hr 59min 44seconds

• Andre slept around 8:15pm and woke up 4:30am. Find the time he spent sleeping.

Solution

In this case we are moving from p.m to a.m, so we are changing only a.m by adding 12 to it.

8:15 p.m = 8 hrs 15mins

4:30 a.m = 16 hrs 30mins (i.e 4 + 16) Time elapsed will be,

What is the length of time taken on a journey which begins at 8:27a.m and ends at 2:16p.m

Solution

In this case, we are moving from a.m to p.m , so we are changing only p.m 8:27a.m = 8hrs 27 mins

2:16p.m = 14hrs 16mins (i.e 2 + 12)

 

Time taken will be,

Quiz

1. How many minutes are there from 12:15p.m to 3:45pm?
2. School starts at 8am. If Yemi arrived at 7:47am, how many minutes early or late was she?
3. A lesson which takes 1 hour 45minutes starts at 10:35 a.m. what time does the lesson end?

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