Card 5 of 8

Time

12- and 24-hour clocks, bridging the hour, fractions of an hour, month lengths.

← All cardsHow to use this: Time & measurement
12-hour24-hour
12:00 midnight00:00
1:00 am01:00
6:30 am06:30
9:45 am09:45
12:00 noon12:00
12:30 pm12:30
1:00 pm13:00
3:15 pm15:15
6:40 pm18:40
9:05 pm21:05
11:59 pm23:59

The two rules:

  1. Afternoon/evening: add 12. 3:15 pm → 3 + 12 = 15:15
  2. Midnight is 00:00, noon is 12:00. These two are the trap — 12:30 am is 00:30, but 12:30 pm is 12:30.

Adding time — bridge in stages, never add like ordinary numbers:

14:35 + 3 h 48 min → add hours: 17:35 → add up to the hour: +25 min → 18:00 (25 of the 48 used) → add the rest: 48 − 25 = 23 → 18:23

Fractional hours (for speed questions): 15 min = 0.25 h · 20 min = ⅓ h · 30 min = 0.5 h · 45 min = 0.75 h.

45 minutes is 0.75 hours, never 0.45. This single error costs more marks than any other in speed questions.

Month lengths: 30 days hath September, April, June and November; all the rest have 31, except February with 28 (29 in a leap year).