Solving Problems with 12- and 24-Hour Time
Year 5 · Maths · Free — no account needed
Solving Problems with 12- and 24-Hour Time
Two ways to write time
12-hour time uses the numbers 1 to 12, with "am" (before midday) or "pm" (after midday) to show which half of the day it is. 24-hour time uses four digits from 0000 to 2359, with no am or pm needed, because the hours just keep counting up past 12.
Converting 12-hour to 24-hour
For am times from 1 am to 11 am, drop the "am" and write the hour with a leading zero if needed: 7:15 am becomes 07:15. The 12 am hour is the exception: it becomes 00, so 12:15 am becomes 00:15. For pm times (except 12 pm), add 12 to the hour: 3:40 pm becomes 15:40, because 3 + 12 = 15.
Converting 24-hour to 12-hour
From 0000 to 1159, it is morning: add "am" (0900 becomes 9:00 am; 0000 to 0059 becomes 12:00 am to 12:59 am). From 1200 to 1259, it is just after midday: keep the hour and add "pm" (1230 becomes 12:30 pm). From 1300 to 2359, subtract 12 from the hour and add "pm": 1745 becomes 5:45 pm, because 17 − 12 = 5.
Midday and midnight
Midday (12 noon) is written as 12:00 pm in 12-hour time, and as 12:00 in 24-hour time. Midnight is written as 12:00 am in 12-hour time, and as 00:00 in 24-hour time — never 24:00.
Working out elapsed time
To find how much time has passed, it helps to break the journey into parts either side of midday or midnight, rather than subtracting straight across. Count the minutes to the next whole hour or to midday/midnight, then add the whole hours, then add any leftover minutes.
Reading timetables
Timetables usually use 24-hour time to avoid mixing up am and pm. Read the departure and arrival times carefully, and check whether a trip crosses midday or midnight before working out how long it takes.
Worked Example
A ferry departs at 10:40 pm and arrives at 1:15 am the next day. How long is the trip? Step 1: Convert both times to 24-hour time so there is no am/pm confusion: 10:40 pm = 22:40, and 1:15 am = 01:15. Step 2: Work out the time from 22:40 to midnight (00:00). From 22:40 to 23:00 is 20 minutes, then 23:00 to 00:00 is 1 more hour — that's 1 hour 20 minutes. Step 3: Work out the time from midnight to 01:15 — that's 1 hour 15 minutes. Step 4: Add the two parts together: 1 hour 20 minutes + 1 hour 15 minutes = 2 hours 35 minutes.
Practice
Convert 4:35 pm to 24-hour time.
Flashcards
What does "am" mean?
Any time from midnight up to (but not including) midday.
What does "pm" mean?
Any time from midday up to (but not including) midnight.
How do you convert an am 12-hour time to 24-hour time?
Drop the "am" and write the hour with a leading zero if needed, e.g. 7:15 am = 07:15. The 12 am hour becomes 00: 12:15 am = 00:15.
How do you convert a pm time (except 12 pm) to 24-hour time?
Add 12 to the hour, e.g. 3:40 pm = 15:40 because 3 + 12 = 15.
How do you convert a 24-hour time of 1300 or more back to 12-hour time?
Subtract 12 from the hour and add "pm", e.g. 1745 = 5:45 pm because 17 − 12 = 5.
How is midday written in 24-hour time, and how is midnight written?
Midday is 12:00; midnight is 00:00 (never 24:00).
What is a good strategy for elapsed time that crosses midday or midnight?
Break the time into parts either side of midday/midnight, then add the parts together.
All 14 practice questions
Convert 4:35 pm to 24-hour time.
- 12:35
- 04:35
- 16:45
- 16:35
Show the answer to question 1
Answer: 16:35
4 + 12 = 16, so 4:35 pm = 16:35.
Convert 09:05 to 12-hour time.
- 9:50 am
- 9:05 am
- 9:05 pm
- 21:05
Show the answer to question 2
Answer: 9:05 am
09:05 is less than 1300, so it stays 9:05 am.
Convert 11:50 pm to 24-hour time.
- 23:05
- 13:50
- 23:50
- 11:50
Show the answer to question 3
Answer: 23:50
11 + 12 = 23, so 11:50 pm = 23:50.
How is midnight written in 24-hour time?
- 00:01
- 12:00
- 24:00
- 00:00
Show the answer to question 4
Answer: 00:00
Midnight is the very start of the day, so it is written as 00:00, never as 24:00.
A clock shows 12:00 pm. What is this in 24-hour time?
- 12:00
- 00:00
- 13:00
- 11:00
Show the answer to question 5
Answer: 12:00
12:00 pm is midday, which is written as 12:00 in 24-hour time.
A hike starts at 11:15 am and finishes at 1:05 pm. How long was the hike?
- 1 hour 10 minutes
- 1 hour 50 minutes
- 2 hours 20 minutes
- 1 hour 40 minutes
Show the answer to question 6
Answer: 1 hour 50 minutes
11:15 am to 12:00 pm is 45 minutes, then 12:00 pm to 1:05 pm is 1 hour 5 minutes, giving 1 hour 50 minutes.
A flight departs at 11:40 pm and lands at 2:20 am the next day. How long was the flight?
- 1 hour 40 minutes
- 3 hours 0 minutes
- 2 hours 40 minutes
- 2 hours 20 minutes
Show the answer to question 7
Answer: 2 hours 40 minutes
11:40 pm to midnight is 20 minutes, then midnight to 2:20 am is 2 hours 20 minutes, giving 2 hours 40 minutes.
The Number 3 bus leaves the depot at 07:15 and arrives at the school at 07:50; the Number 8 bus leaves the depot at 07:40 and arrives at the school at 08:10. Which bus takes less time to reach the school?
- They take the same time
- The Number 8 bus
- The Number 3 bus
- Cannot tell from the timetable
Show the answer to question 8
Answer: The Number 8 bus
07:15 to 07:50 is 35 minutes, but 07:40 to 08:10 is only 30 minutes, so the Number 8 bus is faster.
A market opens at 8:30 am and stays open for 6 hours 45 minutes. What time does it close?
- 3:15 am
- 2:45 pm
- 2:15 pm
- 3:15 pm
Show the answer to question 9
Answer: 3:15 pm
8:30 am plus 6 hours 45 minutes reaches 15:15, which is 3:15 pm.
Movie A starts at 6:50 pm and finishes at 9:05 pm; Movie B starts at 7:15 pm and finishes at 9:40 pm. Which movie is longer?
- Cannot tell
- Movie A
- Movie B
- They are the same length
Show the answer to question 10
Answer: Movie B
Movie A runs 2 hours 15 minutes but Movie B runs 2 hours 25 minutes, so Movie B is longer.
A bakery worker finishes a shift at 12:30 am after working for 7 hours 45 minutes. What time did the shift start?
- 4:45 am
- 4:45 pm
- 5:15 pm
- 5:45 pm
Show the answer to question 11
Answer: 4:45 pm
12:30 am is 00:30; going back 7 hours 45 minutes reaches 16:45 the previous day, which is 4:45 pm.
A library is open from 9:45 am to 5:20 pm. How many hours and minutes is it open?
- 7 hours 25 minutes
- 7 hours 35 minutes
- 6 hours 35 minutes
- 7 hours 45 minutes
Show the answer to question 12
Answer: 7 hours 35 minutes
9:45 am to 12:00 pm is 2 hours 15 minutes, then 12:00 pm to 5:20 pm is 5 hours 20 minutes, giving 7 hours 35 minutes.
The morning ferry leaves the wharf at 06:50 and arrives at the island at 07:35; the afternoon ferry leaves the wharf at 13:10 and arrives at the island at 14:05. How much longer is the afternoon trip than the morning trip?
- 15 minutes
- 5 minutes
- 55 minutes
- 10 minutes
Show the answer to question 13
Answer: 10 minutes
The morning trip takes 45 minutes and the afternoon trip takes 55 minutes, so the afternoon trip is 10 minutes longer.
The Express bus leaves Town Hall at 15:40 and arrives at the Beach at 16:55; the Local bus leaves Town Hall at 15:20 and arrives at the Beach at 16:50. Which trip is shorter?
- The Express bus
- They take the same time
- The Local bus
- Cannot tell from the timetable
Show the answer to question 14
Answer: The Express bus
The Express bus trip takes 1 hour 15 minutes, but the Local bus trip takes 1 hour 30 minutes, so the Express bus is shorter.
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