NCERT Class 5 Maths · Chapter 12
Racing Seconds
Time in hours, minutes, and seconds: elapsed time, the 24-hour clock, conversions, and start and end times.
📌 What you’ll learn in this chapter
- Finding how much time has passed (elapsed time)
- The second, a tiny unit of time (60 seconds = 1 minute)
- Reading the seconds hand on a clock
- The 12-hour (a.m./p.m.) and 24-hour clock
- Converting hours ↔ minutes ↔ seconds, and finding start or end times
🏃 Let’s Begin: A Photo Finish!
In the Sports Day 100 m race, Aman and Jaspreet crossed the line almost together. Both finished “in 16 seconds”… but the stopwatch showed Aman at 16.2 s and Jaspreet at 16.5 s. Aman won!
For short events like races, seconds (and even parts of seconds) matter.
⏰ Part 1: Units of Time
| Unit | Relation | Things that take about this long |
|---|---|---|
| Second (s) | 60 s = 1 min | Blinking, clapping, sneezing, snapping fingers |
| Minute (min) | 60 min = 1 hour | Brushing teeth, washing hands, a phone call |
| Hour (h) | 24 h = 1 day | A school period is less; a movie is 2–3 hours |
On a clock, the thin fast seconds hand goes all the way round in 60 seconds. Each small mark is 1 second, and each number is 5 seconds.
Example: The seconds hand moves from 3 to 9. How many seconds is that?
6 numbers × 5 = 30 seconds
⌛ Part 2: How Much Time Has Passed?
Jump method (count on the clock)
Kabir started homework at 4:40 p.m. and finished at 6:15 p.m.
4:40 → 5:00 = 20 min
5:00 → 6:00 = 1 hour
6:00 → 6:15 = 15 min
Total = 1 hour 35 minutes
💡 Jump to the next “o’clock” first
Jump to the next full hour, then jump whole hours, then jump the remaining minutes. It’s much easier than subtracting.
Finding the end time
A train leaves at 9:50 a.m. and the journey takes 2 h 25 min.
9:50 + 2 h = 11:50 → + 10 min = 12:00 noon → + 15 min = 12:15 p.m.
Finding the start time (count backwards)
A match ended at 5:10 p.m. after 1 h 30 min.
5:10 − 1 h = 4:10 → − 10 min = 4:00 → − 20 min = 3:40 p.m.
🕛 Part 3: The 24-Hour Clock
Trains, buses, and phones often use the 24-hour clock. Nothing is repeated, so there’s no need for a.m. or p.m.
- Morning (a.m.): Keep the same numbers. 7:15 a.m. = 07:15 hours
- After noon (p.m.): Add 12 to the hour. 4:20 p.m. = 4 + 12 = 16:20 hours
- 12 noon = 12:00 hours · 12 midnight = 00:00 hours
⚠️ Common mistake
Writing 9:30 p.m. as 19:30 ❌ (that’s 7:30 p.m.)
✅ 9 + 12 = 21, so 9:30 p.m. = 21:30 hours
✅ 9 + 12 = 21, so 9:30 p.m. = 21:30 hours
Going back: 18:45 hours → 18 − 12 = 6 → 6:45 p.m.
🔁 Part 4: Converting Time
| To change | Do this | Example |
|---|---|---|
| Hours → minutes | × 60 | 3 h = 180 min |
| Minutes → seconds | × 60 | 4 min = 240 s |
| Minutes → hours and minutes | Take out groups of 60 | 135 min = 2 h 15 min |
| Seconds → minutes and seconds | Take out groups of 60 | 200 s = 3 min 20 s |
2 h 35 min = 120 + 35 = 155 min
7 min 12 s = 420 + 12 = 432 s
⚠️ Common mistake
Thinking 1 hour = 100 minutes, so 1 h 50 min + 20 min = 1 h 70 min ❌
✅ 70 min = 1 h 10 min, so the answer is 2 h 10 min.
✅ 70 min = 1 h 10 min, so the answer is 2 h 10 min.
❌ Common Mistakes to Avoid
Mixing up the hour and minute hands
✅ Short hand = hours, long hand = minutes, thin hand = seconds.
✅ Short hand = hours, long hand = minutes, thin hand = seconds.
Forgetting to change a.m. to p.m. after 12 noon
✅ 11:30 a.m. + 1 h = 12:30 p.m.
✅ 11:30 a.m. + 1 h = 12:30 p.m.
Subtracting times like normal numbers (5:10 − 3:40 = 1:70)
✅ Use the jump method.
✅ Use the jump method.
Writing 24-hour time without the zero
✅ 7:05 a.m. = 07:05 hours.
✅ 7:05 a.m. = 07:05 hours.
✏️ Practice Time
Try these on your own first, then check your answer below each question.
Q1. Seconds or minutes: (a) tying a shoelace (b) cooking rice (c) clapping once
✅ Answer(a) seconds (b) minutes (c) seconds
Q2. A class starts at 10:25 a.m. and ends at 11:10 a.m. How long is it?
✅ Answer10:25 → 11:00 = 35 min, then 11:00 → 11:10 = 10 min. Total = 45 min
Q3. Write in 24-hour time: (a) 6:05 a.m. (b) 3:50 p.m. (c) 11:15 p.m.
✅ Answer(a) 06:05 (b) 15:50 (c) 23:15 hours
Q4. Convert: (a) 4 h 5 min = __ min (b) 250 s = __ min __ s
✅ Answer(a) 245 min (b) 4 min 10 s
Q5. A bus leaves at 21:40 hours and reaches at 01:15 hours the next day. How long was the journey?
✅ Answer21:40 → 22:00 = 20 min · 22:00 → 01:00 = 3 h · 01:00 → 01:15 = 15 min. Total = 3 h 35 min
Q6. A movie of 2 h 40 min ends at 9:10 p.m. When did it start?
✅ Answer9:10 − 2 h = 7:10, then − 40 min = 6:30 p.m.
📘 NCERT Textbook Activity Help
Hints and answers for the activities in the textbook, page by page. Try each one yourself before looking at the answer!
Page 155 · Raghav’s yogaStart, finish, and elapsed time
✅ Answer
1. The long (orange) hand is on 7 and the short hand is between 5 and 6, so he started at about 5:35 a.m.
2. The long hand is on 11 and the short hand is close to 6, so he finished at about 5:55 a.m.
3. 20 minutes
4. (a) 27 min (b) 5 hours (c) 2 h 15 min
5. (a) Rani (2 h 10 min) (b) Raghav (1 h 20 min)
Page 156 · 24-hour clock2. The long hand is on 11 and the short hand is close to 6, so he finished at about 5:55 a.m.
3. 20 minutes
4. (a) 27 min (b) 5 hours (c) 2 h 15 min
5. (a) Rani (2 h 10 min) (b) Raghav (1 h 20 min)
Fill and match
✅ Answer
Q6: 08:35 hours = 08:35 a.m. · 11:55 a.m. = 11:55 hours · 05:30 p.m. = 17:30 hours · 09:35 p.m. = 21:35 hours
Q7: 06:30 a.m. → 06:30 hours · 08:45 p.m. → 20:45 hours · 11:45 p.m. → 23:45 hours · 04:30 a.m. → 04:30 hours · 07:30 p.m. → 19:30 hours · 01:30 a.m. → 01:30 hours
Page 157 · School RaceQ7: 06:30 a.m. → 06:30 hours · 08:45 p.m. → 20:45 hours · 11:45 p.m. → 23:45 hours · 04:30 a.m. → 04:30 hours · 07:30 p.m. → 19:30 hours · 01:30 a.m. → 01:30 hours
Who won?
✅ AnswerThe winner (1st place) took 1 min 55 s. 2nd place took 1 min 56 s, and 3rd took 1 min 57 s. Everyone took 1 minute and some seconds. The winner was just 1 second faster!
Seconds: blinking, switching lights on and off, counting 1–20, filling a glass, sitting down, drinking a glass of water, snapping fingers, washing hands (about 20–40 s).
Minutes: melting an ice cube, making a phone call.
Page 158 · Let Us FindSeconds: blinking, switching lights on and off, counting 1–20, filling a glass, sitting down, drinking a glass of water, snapping fingers, washing hands (about 20–40 s).
Minutes: melting an ice cube, making a phone call.
Your own timings
✅ AnswerUse a stopwatch or the seconds hand of a clock. Your answers will differ from your friends’. For example, most children write “FRIEND” in about 3–5 seconds and run 100 m in about 15–25 seconds.
Page 159 · Let Us DoReading the seconds hand
✅ Answer1. The seconds hand moved from 12 to 6 → 30 sec
2. From 12 to 7 → 35 sec
3. From 9 to 12 → 15 sec
4. The seconds hand is at the same place, but the minute hand moved one mark, so it made a full turn → 60 sec
Page 160 · Draw the seconds hand2. From 12 to 7 → 35 sec
3. From 9 to 12 → 15 sec
4. The seconds hand is at the same place, but the minute hand moved one mark, so it made a full turn → 60 sec
Where does it end?
✅ AnswerEach number is 5 seconds, so move the hand forward from its start position by: 20 s → 4 numbers · 30 s → 6 numbers (half a turn) · 60 s → a full turn (back to the start) · 40 s → 8 numbers
Pages 161–162 · ConversionsHours, minutes, and seconds
✅ Answer
(a) 2 hr · 4 hr = 240 min · 7 hr = 420 min · 8 hr = 480 min · 9 hr = 540 min · 11 hr = 660 min · 12 hr = 720 min
(b) (i) 70 (ii) 165 (iii) 195 (iv) 260 (v) 1 h 15 min (vi) 2 h 30 min (vii) 3 h 40 min (viii) 6 h 30 min
(c) 2 min · 5 min = 300 s · 10 min = 600 s · 15 min = 900 s · 20 min · 25 min
(i) 5 min 20 s (ii) 3 min 45 s (iii) 11 min 40 s (iv) 16 min 40 s (v) 613 s (vi) 248 s (vii) 940 s
Q2: 4 × 50 = 200 min = 3 h 20 min
Q3: 1 hour 5 minutes
Page 163 · Start and end times(b) (i) 70 (ii) 165 (iii) 195 (iv) 260 (v) 1 h 15 min (vi) 2 h 30 min (vii) 3 h 40 min (viii) 6 h 30 min
(c) 2 min · 5 min = 300 s · 10 min = 600 s · 15 min = 900 s · 20 min · 25 min
(i) 5 min 20 s (ii) 3 min 45 s (iii) 11 min 40 s (iv) 16 min 40 s (v) 613 s (vi) 248 s (vii) 940 s
Q2: 4 × 50 = 200 min = 3 h 20 min
Q3: 1 hour 5 minutes
Word problems
✅ Answer4. 08:00 p.m. 5. 08:30 p.m. 6. 12:40 p.m. 7. 07:30 p.m. 8. 06:40 p.m. 9. 01:05 p.m. 10. 05:00 a.m. (the next day)
👨👩👧 Tips for Parents
- Use a phone stopwatch for fun challenges: “How many jumps can you do in 30 seconds?”
- Read train or bus timings together and change them to a.m./p.m.
- Ask: “Your cartoon starts at 5:45 and lasts 25 minutes. When does it end?”