Seconds, the 24-hour clock and timetables · Usually met around P3
Reading timetables
Two times in one column: count to the o'clock first.
How to do it
Method
Two times in one column: count to the o'clock first
08:50 → 09:00 → 09:17: 10 + 17 = 27
Another way
Minutes after midnight
557 − 530 = 27
In full
Each row of a timetable is a stop and each column is one bus, with times on the 24-hour clock. To find how long a bus takes from stop A to stop B, take the two times in the same column and count from the earlier to the later: to the next o'clock first, then the rest. 08:50 → 09:00 is 10 minutes, 09:00 → 09:17 is 17 more: 27 minutes. To find a wait, look along your stop's row for the first time after now, then count the minutes. To arrive by a certain time, look along the arrival stop's row for the last bus not later than it. Very short times can be less than a second, written as decimals: 0.3 s is shorter than 1 s, and in a race fewer seconds is faster. Another way: turn both times into minutes after midnight and take away: 9 × 60 + 17 = 557, 8 × 60 + 50 = 530, 557 − 530 = 27.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Look at the bus timetable. Ming reaches stop A at 06:06. How many minutes until the next bus leaves?
Show the answer and working
Answer: 4 minutes
Along stop A's row, the first bus after 06:06 leaves at 06:10: a 4-minute wait.
Example 2
Look at the bus timetable. Bus 3 takes 12 minutes from stop A to stop C.
True or false?
Show the answer and working
Answer: False
For bus 3, count from its time at stop A to its time at stop C: 22 minutes.
Example 3
Tsz-ching runs 50 m in 9.2 s and Ming in 9.4 s. How many seconds faster is Tsz-ching?
Show the answer and working
Answer: 0.2 s
The whole seconds match, so look at the digit after the point: from 9.2 to 9.4 is 2 lots of 0.1 s, so 0.2 s, less than a second faster.
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