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Math · Measurement & Time
Elapsed Time: Read Clocks, Cross the Hour, Check a Schedule
Grade 3–4 time reasoning: calculate elapsed minutes across an hour, work backward, compare swim and school schedules, and explain your answer with a timeline.
The idea
An end time, a start time and an elapsed duration are different quantities. Before calculating, circle what the question asks: When? Or for how long?
A reliable way to cross an hour is to break the interval at :00. For example, 2:45 to 3:20 is 15 minutes to 3:00, then 20 more minutes, or 35 minutes.
Sixty minutes make an hour, so 85 minutes is one hour and 25 minutes. It is not 1.85 hours. Minutes in clock times do not use base ten.
A clock diagram or timeline lets you check: move forward to calculate an end time, and move backward to verify the start.
Worked examples
Example 1 · Cross the hour
Swimming starts at 4:45 and ends at 5:20. How long is training?
- 4:45 → 5:00 is 15 minutes.
- 5:00 → 5:20 is 20 minutes.
- 15 + 20 = 35 minutes; check: 4:45 + 35 minutes = 5:20.
35 minutes.
Example 2 · Add more than an hour
A coach schedules a 75-minute practice beginning at 5:35.
- 75 minutes = 1 hour + 15 minutes.
- 5:35 + 1 hour = 6:35.
- 6:35 + 15 minutes = 6:50.
Practice ends at 6:50.
Example 3 · Count backward
You must arrive 15 minutes before a 9:05 activity.
- 9:05 − 5 minutes = 9:00.
- 9:00 − 10 minutes = 8:50.
- Check: 8:50 + 15 minutes = 9:05.
Arrive by 8:50.
Example 4 · Duration with a break
A 45-minute lesson includes a 5-minute water break.
- Elapsed session time is 45 minutes, including the break.
- Actual practice time is 45 − 5 = 40 minutes.
- Do not subtract the break if asked for the total session length.
40 minutes of practice; 45 minutes elapsed.
Example 5 · After midnight
A journey runs from 11:45 p.m. to 12:20 a.m. the next day.
- 11:45 p.m. → midnight is 15 minutes.
- Midnight → 12:20 a.m. is 20 minutes.
- 15 + 20 = 35 minutes; the date changes but the duration remains positive.
35 minutes.
Common mistakes
These are tempting because they use familiar operations. Check what the question is actually measuring.
Why this fails: Clock minutes restart at 00 after 59, so the correct time is 4:10.
Why this fails: Count from 2:45 to 3:00, then 3:00 to 3:20.
Why this fails: An hour has 60 minutes, but times use minutes 00–59.
Why this fails: Clarify whether the question asks about total elapsed time or active time.
Why this fails: An accurate time answer may need the day as well.
Foundation
Foundation practice
Read exact times and count in minutes
1. The clock moves from 2:10 to 2:35. How many minutes pass?
2. A lesson starts at 3:05 and lasts 20 minutes. When does it finish?
3. A library visit starts at 9:00 and lasts 45 minutes. When does it finish?
4. From 7:40 to 7:55, how long do you wait?
5. A game begins at 4:30 and ends at 5:00. What is its duration?
6. Warm-up begins at 10:15. What time is 15 minutes later?
7. It is 11:50. How many minutes until noon?
8. A ride begins at 1:10 and lasts 50 minutes. When does it end?
9. You must arrive 20 minutes before 8:00. At what time should you arrive?
Core
Core practice
Split time into the next hour and count what remains
10. How long from 2:45 to 3:20?
11. A bus leaves at 9:35 and travels for 50 minutes. What time does it arrive?
12. How long is the interval from 4:50 to 5:35?
13. Class begins at 8:55 and ends at 9:40. How long is class?
14. A workshop begins at 3:25 and lasts 65 minutes. What time does it end?
15. Training begins at 6:40 and ends at 7:05. What is the elapsed time?
16. A film starts at 7:15 and lasts 85 minutes. When does it end?
17. How long from 10:50 to 11:30?
18. Lunch starts at 11:25 a.m. and lasts 95 minutes. When does lunch end?
Transfer
Transfer practice
Combine durations and identify relevant information
19. A swim lesson runs from 4:10 to 4:55. Getting changed takes 15 more minutes. When can the swimmer leave?
20. The school bus leaves at 8:15, and the trip lasts 35 minutes. How early is arrival for a 9:00 event?
21. A practice runs from 5:20 to 6:05, including a five-minute rest. How many minutes are spent practising?
22. A visit has 12 minutes of reading, 5 minutes of break and 18 minutes of writing. What is the total duration?
23. A train is scheduled for 3:25 but arrives at 3:40. How many minutes late is it?
24. An activity begins at 11:50 a.m. and ends at 12:30 p.m. What is its duration?
25. An appointment is at 4:40. You should check in 20 minutes early. When should you arrive?
26. Two drills take 18 minutes each, with a 6-minute break between them. How much time is needed?
27. The group has 50 minutes. It uses 42 minutes for drills and break. How much spare time remains?
Challenge
Challenge practice
Work backwards, compare sessions and cross noon or midnight
28. A night train leaves at 11:35 p.m. and arrives at 12:10 a.m. the next day. How long is the ride?
29. A train leaves at 10:45 p.m. and travels 90 minutes. When does it arrive?
30. A field trip begins at 9:10 a.m. and ends at 2:05 p.m. How long is it?
31. You leave at 8:35. The walk takes 12 minutes and the bus departs at 8:50. How much waiting time is there?
32. Swim warm-up starts at 6:15 a.m. The drive takes 40 minutes and you want a 10-minute arrival buffer. When should you leave?
33. A swimmer finishes in 1 minute 18 seconds, then 1 minute 12 seconds. By how much is the second swim faster?
34. The timetable lists 15:25. What is this in 12-hour time?
35. Session A is 6:05–7:20. Session B is 6:50–7:35. How much longer is A?
36. A clock runs three minutes fast and displays 10:08. What is the actual time?
Answer key
- 1. 25 minutes
From minute 10 to minute 35 is 35 − 10 = 25 minutes. - 2. 3:25
5 + 20 = 25 minutes past 3. - 3. 9:45
Count 45 minutes forward from 9:00. - 4. 15 minutes
55 − 40 = 15 minutes. - 5. 30 minutes
Half an hour is 30 minutes. - 6. 10:30
15 minutes after quarter past 10 is half past 10. - 7. 10 minutes
The next hour starts after 60 − 50 = 10 minutes. - 8. 2:00
The remaining 50 minutes complete the hour. - 9. 7:40
Count 20 minutes backward from 8:00. - 10. 35 minutes
15 minutes to 3:00 plus 20 minutes to 3:20 is 35. - 11. 10:25
25 minutes reach 10:00; another 25 reach 10:25. - 12. 45 minutes
10 minutes to 5:00 plus 35 more minutes. - 13. 45 minutes
5 minutes to 9:00 plus 40 minutes. - 14. 4:30
65 minutes is 1 hour 5 minutes. - 15. 25 minutes
20 minutes to 7:00 and 5 more. - 16. 8:40
85 minutes equals 1 hour 25 minutes. - 17. 40 minutes
10 minutes to 11:00 and 30 more. - 18. 1:00 p.m.
95 minutes is 1 hour 35 minutes: 11:25 → 12:25 → 1:00 p.m. - 19. 5:10
The lesson finishes at 4:55; another 15 minutes reaches 5:10. - 20. 10 minutes early
Arrival is 8:50, 10 minutes before 9:00. - 21. 40 minutes
45 elapsed minutes minus a 5-minute rest. - 22. 35 minutes
12 + 5 + 18 = 35. - 23. 15 minutes
40 − 25 = 15 minutes after the scheduled time. - 24. 40 minutes
10 minutes to noon, then 30 more. - 25. 4:20
Subtract 20 minutes from 4:40. - 26. 42 minutes
18 + 6 + 18 = 42 minutes. - 27. 8 minutes
50 − 42 = 8 minutes. - 28. 35 minutes
25 minutes to midnight plus 10 minutes after midnight. - 29. 12:15 a.m. next day
One hour reaches 11:45 p.m.; another 30 minutes passes midnight. - 30. 4 hours 55 minutes
9:10 → 2:10 is five hours; end is five minutes earlier. - 31. 3 minutes
You arrive at 8:47 and wait until 8:50. - 32. 5:25 a.m.
Subtract 10 minutes to arrive by 6:05, then 40 more minutes. - 33. 6 seconds
Both have one minute, so subtract 12 from 18 seconds. - 34. 3:25 p.m.
15 − 12 = 3; the minutes remain 25. - 35. 30 minutes
A lasts 75 minutes; B lasts 45; difference is 30. - 36. 10:05
A fast clock shows a time three minutes ahead, so subtract three minutes.