Time

60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day
7 days = 1 week
52 weeks = 1 year

Introduced by Pope Gregory XIII in October 1582, the Gregorian calendar replaced the Julian calendar .

Adopted in Great Britain in September 1752 — 2nd September 1752 was immediately followed by 14th September 1752.

Months of the year:

January — 31 days
February — 28 days (29 in leap year)
March — 31 days
April — 30 days
May — 31 days
June — 30 days
July — 31 days
August — 31 days
September — 30 days
October — 31 days
November — 30 days
December — 31 days

12‑hour clock times are written with:
• am to represent morning
• pm to represent afternoon
A colon is used to separate minutes.

9:30 am — half past nine in the morning.
9:37 pm — 23 minutes to ten in the evening.

24‑hour clock times are written with two digits for the hour and a colon to separate minutes.

09:30 — half past nine in the morning.
21:37 — 23 minutes to ten in the evening.

Military usage of the 24‑hour clock:
• drops the colon
• adds the word hrs

09 30 hrs — half past nine in the morning.
21 37 hrs — 23 minutes to ten in the evening.

To convert from 12‑hour clock to 24‑hour clock:

• Drop the am or pm
• Add 12 to the hour if the time is in the afternoon (pm)

9:30 am → 09:30 → 09 30 hrs
3:15 pm → 15:15 → 15 15 hrs

• Subtract 12 from the hours if the time is between 13:00 and 24:00
• Drop the hrs if it was included
• Add am if the time is between 00:00 and 11:59
• Add pm if the time is between 12:01 and 24:00

03:15 → 3:15 am
23:23 → 11:23 pm
11 27 hrs → 11:27 am
21 00 hrs → 9 pm

Calculate the number of minutes from start time to next hour, then number of complete hours, then number of minutes from final hour to end time

\[ \text{ start} \] \[ 09{:}45 \;\xrightarrow{\text{15 minutes}}\; 10{:}00 \] \[ 10{:}00 \;\xrightarrow{\text{7 hours}}\; 17{:}00 \] \[ 17{:}00 \;\xrightarrow{\text{38 minutes}}\; 17{:}38 \quad \text{finish} \] \[ 7 \text{ hours } 53 \text{ minutes} \]

Do not use your calculator unless you are using the Deg/Hour/Min function. Otherwise your answer will not be converted properly.

Calculate the time difference between:
a) 11:07 and 11:30  b) 11:07 and 12:00

Although tempting to use, the calculator gives the wrong answer for part b :

This is because the calculator is working in base 10 and time is base 60

Correct way

 

 

1 hour is 60 minutes.

So:

0.1 of an hour is 6 minutes.

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