Time is base-60, not base-10
There are seconds in a minute and minutes in an hour, so time does not add like ordinary decimals. min min min h min — you carry at , not at .
24-hour clock: no a.m./p.m. ambiguity
In the 24-hour clock, a.m. is written and p.m. is . To convert an afternoon/evening 12-hour time to 24-hour, add to the hours (so p.m. ); midnight is and noon is .
Find a duration by counting up in chunks
To find a duration, count from the start time up to the next whole hour, then add whole hours, then the remaining minutes — e.g. is min, then is min, then is min, total min. This avoids the errors of subtracting clock times like decimals.
Drawn from real examiner reports.
Subtracting times as if they were decimals
Working out as treats the minutes as base- and is wrong. You must borrow (not ) from the hours column: min minus min needs a borrowed hour, giving min and h h min.
Going the wrong way across time zones
Travelling east the local clock is ahead (later); travelling west it is behind (earlier). Adding when you should subtract (or vice versa) sends the answer the wrong way. Note the sign of the offset: a city at UTC is hours ahead of UTC.
Converting a.m./p.m. to 24-hour wrongly
Add only to afternoon/evening times: p.m. , but a.m. stays (writing it as is wrong). Midnight is and noon is .
Not splitting a duration at midnight
A journey from to is not found by subtracting straight across (that gives nonsense). Split at midnight: minutes to , plus minutes after — here minutes.
Writing 85 minutes instead of carrying
When adding times, minutes must be carried as hour minutes, so , not . Carry every minutes into the hours column.
Read timetables down each column
On a timetable each column is one service; read down a column for one journey. If a journey crosses midnight, the duration is (minutes to ) (minutes after ) — don't subtract straight across.
Add durations: hours first, then minutes
To add a duration, add the whole hours first, then the minutes, carrying every minutes into the hours. : , then min .
Time difference = difference of UTC offsets
The time gap between two places is the difference of their UTC offsets — e.g. UTC and UTC differ by hours. Then apply it the right way: east is ahead, west is behind.
The syllabus takes 1 year = 365 days. Time is base-60: you carry at , not at . So minutes is min h min.
How do you write 3.15 p.m. in the 24-hour clock?
A train leaves a station at and arrives at the next station at . How many minutes does the journey take?
