TalentJR

Racing Seconds – Class 5 Maths Chapter 12 Notes & NCERT PDF

Class 5MathematicsChapter 12NCERT book: Maths Mela - Mathematics Class 5

Notes and a simple summary of Chapter 12 of the NCERT Class 5 Mathematics book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

🎧 Listen to the content

Chapter 12: Racing Seconds

Introduction

Raghav practises yoga in the morning and wants to know how long he practised. Akira, Sunita and Mary take part in a 200 m walking race — their stopwatches show 01:55, 01:56 and 01:57 (minutes : seconds). All three took 1 minute and something, so who won? To tell, we need a smaller unit — the second. This chapter is all about measuring time precisely, converting between hours, minutes and seconds, 12-hour and 24-hour clocks, and finding elapsed (passed) time.

1 hour = 60 minutes 1 minute = 60 seconds

Key Ideas

1. Elapsed time

Elapsed time is the time that passes between a start time and an end time.

  • 01:15 p.m. to 01:42 p.m. → 27 minutes
  • 03:18 p.m. to 08:18 p.m. → 5 hours
  • 09:15 a.m. to 11:30 a.m. → 2 hours 15 minutes

    • Comparing durations: Raghav painted for 1 h 20 min, Rani for 2 h 10 min, Ritu for 1 h 35 min — Rani took the longest, Raghav the least.

    2. 12-hour and 24-hour formats

  • In the 24-hour format, the hours after noon continue as 13, 14 … 23. Add 12 to p.m. hours.
  • 05:30 a.m. = 05:30 hours; 02:30 p.m. = 14:30 hours; 05:30 p.m. = 17:30 hours
  • 09:35 p.m. = 21:35 hours; 11:45 p.m. = 23:45 hours; 01:30 a.m. = 01:30 hours
  • 08:35 hours = 08:35 a.m.; 20:45 hours = 08:45 p.m.

    • 3. Seconds — measuring short events

    In the race each child took 1 minute, but the seconds show the small difference. The winner is the child with the least time: 01:55 (1 min 55 sec).

    Activities like blinking, snapping fingers, sitting down, switching a light on and off take seconds; making a phone call or an ice cube melting take minutes.

    On a clock, 60 movements of the seconds hand move the minute hand by one minute.

    4. Converting units (double number line)

  • 1 hour = 60 min → 2 hours = 120 min → 4 hours = 240 min → 7 hours = 420 min → 9 hours = 540 min
  • Going back: 480 min = 8 hours, 660 min = 11 hours, 720 min = 12 hours
  • 1 hour 10 min = 60 + 10 = 70 min
  • 2 hours 45 min = 120 + 45 = 165 min
  • 150 min = 120 + 30 = 2 h 30 min; 390 min = 6 h 30 min
  • 320 sec = 300 + 20 = 5 min 20 sec; 1,000 sec = 16 min 40 sec
  • 10 min 13 sec = 600 + 13 = 613 sec

    • Worked Examples

    Example 1: Raghav studies 4 subjects for 50 minutes each.

    Total = 4 × 50 = 200 min = 180 + 20 = 3 hours 20 minutes.

    Example 2: Raghu left at 08:00 hours and reached Nana ji’s house at 09:05 hours.

    08:00 → 09:00 is 1 hour, then 5 more minutes → 1 hour 5 minutes.

    Example 3: Jyoti went to play at 06:15 p.m. and came back after 1 h 45 min.

    06:15 + 1 h = 07:15; 07:15 + 45 min = 08:00 p.m.

    Example 4: Ragini finished homework at 09:40 p.m. after 1 h 10 min. When did she start?

    Count back: 09:40 − 1 h = 08:40; 08:40 − 10 min = 08:30 p.m.

    Example 5: It is 08:35 p.m. What time after 8 h 25 min?

    08:35 p.m. + 8 h = 04:35 a.m.; + 25 min = 05:00 a.m. (the next day)

    Maths Words

  • Second (सेकंड), Minute (मिनट), Hour (घंटा)
  • Elapsed time (बीता हुआ समय)
  • Stopwatch (विराम घड़ी)
  • 12-hour format (12-घंटे का प्रारूप) with a.m. (पूर्वाह्न) / p.m. (अपराह्न)
  • 24-hour format (24-घंटे का प्रारूप)
  • Duration (अवधि)
  • Double number line (दोहरी संख्या रेखा)
  • Estimate (अनुमान लगाना)

    • Maths in Daily Life

  • Railway, bus and flight timings use the 24-hour clock.
  • Races and sports use seconds (even parts of a second!).
  • Planning homework, playtime and sleep needs elapsed time.

    • Common Mistakes

  • Treating time like ordinary numbers: 1 h 50 min + 20 min is 2 h 10 min, not 1 h 70 min.
  • Forgetting to add 12 for p.m. times in the 24-hour format (05:30 p.m. is 17:30, not 05:30).
  • In a race, thinking the bigger time wins — the smallest time wins.
  • Crossing noon or midnight and forgetting to switch a.m./p.m.

    • Practice Tips

  • Solve time problems orally by jumping on a clock: first whole hours, then minutes.
  • Use a real stopwatch: count how many times you skip a rope in 10 seconds, or how long you take to write the word FRIEND.
  • Estimate first, then check: how many hops on one leg in a minute?

    • 💡 Key Learning Points

    • ✓1 hour = 60 minutes and 1 minute = 60 seconds; seconds help us measure short events precisely, as in a race.
    • ✓Elapsed time can be found by counting on from the start time — first hours, then minutes.
    • ✓In the 24-hour format, p.m. hours are written by adding 12 (02:30 p.m. = 14:30 hours).
    • ✓Hours, minutes and seconds can be converted using multiplication and division by 60 (double number line).
    • ✓Start or end times can be found by counting forward or backward from a known time and duration.

    👨‍🏫 Teaching Tips

    • →Hold a class 200 m walk (or a short race) with a stopwatch and let children decide who won from times like 01:55, 01:56, 01:57.
    • →Ask children to sort activities (blinking, phone call, washing hands) into ‘seconds’ or ‘minutes’ before timing them.
    • →Use a large demonstration clock to show that 60 moves of the seconds hand move the minute hand once.
    • →Draw double number lines on the board for hours↔minutes and minutes↔seconds conversions.
    • →Bring a railway or bus timetable to practise reading 24-hour times.
    • →Encourage oral ‘jump’ strategies on a number line rather than column subtraction, as the textbook suggests.
    • →Let children record the time they take for a small task (writing FRIEND, running 100 m) and compare.

    📋 Assessment Questions

    1. Can the child find elapsed time between two given times (e.g. 09:15 a.m. to 11:30 a.m.)?
    2. Can the child convert 12-hour times to 24-hour format and back?
    3. Can the child convert 2 h 45 min to minutes and 320 sec to minutes and seconds?
    4. Can the child find the finishing or starting time when the duration is given?
    5. Can the child explain why seconds are needed to decide the winner of a race?

    Ask the AI tutor about Class 5 Mathematics Chapter 12

    Get question answers, important questions, a quick MCQ quiz or a simple explanation of “Racing Seconds”. Free — sign in with Google.

    How the AI tutor works →

    👩‍🏫 Class 5 Mathematics classes near you — online or at home

    Prefer a real teacher? TalentJR teachers take live online classes anywhere in India and visit homes in selected cities. Tell us what you need and our team will call you with timings and fees.

    • Live online classesSmall groups or 1:1 with a teacher, from home, any city.
    • Teacher at homeA TalentJR teacher visits your home (selected cities).
    • At a centreClasses at a TalentJR partner centre near you, where available.

    Keep learning

    All chapters in Maths Mela - Mathematics Class 5

    1. 1. We the Travellers — I
    2. 2. Fractions
    3. 3. Angles as Turns
    4. 4. We the Travellers — II
    5. 5. Far and Near
    6. 6. The Dairy Farm
    7. 7. Shapes and Patterns
    8. 8. Weight and Capacity
    9. 9. Coconut Farm
    10. 10. Symmetrical Designs
    11. 11. Grandmother’s Quilt
    12. 12. Racing Seconds
    13. 13. Animal Jumps
    14. 14. Maps and Locations
    15. 15. Data Through Pictures