Chapter 12 — Racing Seconds

Chapter 12 of the Class 5 Mathematics NCERT textbook (Maths Mela), "Racing Seconds", introduces seconds as a unit of time and covers reading clocks, converting between hours, minutes, and seconds, and solving elapsed-time problems — download the PDF to practise reading time in 12-hour and 24-hour formats and work through word problems on time intervals.

• Seconds as a Unit of Time — The chapter introduces 'seconds' by having students compare race finish times (1 min 55 sec, 1 min 56 sec, 1 min 57 sec) to show that 1 minute = 60 seconds and that seconds capture small differences that minutes alone cannot express.
• 12-Hour and 24-Hour Clock Formats — Students fill in conversion tables matching times like 05:30 a.m. to 05:30 hours and 02:30 p.m. to 14:30 hours, building familiarity with both formats through matching exercises.
• Converting Between Hours, Minutes, and Seconds — The chapter uses double number lines to practise converting hours to minutes (1 hr = 60 min, so 2 hr = 120 min) and minutes to seconds (1 min = 60 sec), including mixed conversions such as 220 minutes into hours and minutes.
• Elapsed-Time Word Problems — Students solve practical problems — finding how long a picnic lasted, when homework ended given a start time, or what time results after adding a duration — using real-life contexts like a school lunch break or a child travelling to a relative's house.

1. 011 minute = 60 seconds; seconds are used when small time differences matter, such as in a race.
2. 02A school 200 m walking race between Akira, Sunita, and Mary illustrates why seconds are needed — their times were 1 min 55 sec, 1 min 56 sec, and 1 min 57 sec.
3. 03Students estimate whether everyday activities (blinking, washing hands, making a phone call) take seconds or minutes before verifying.
4. 04The 12-hour clock uses a.m./p.m. labels; the 24-hour clock uses four-digit hours — for example, 02:30 p.m. equals 14:30 hours.
5. 05Double number lines are used to convert hours to minutes and minutes to seconds, showing multiplication relationships (x60, x2, etc.).
6. 06Mixed conversions practised include changing 1 hour 10 minutes to 70 minutes and 390 minutes to 6 hours 30 minutes.
7. 07Elapsed-time problems involve finding start times, end times, and total durations using real contexts such as study schedules and outdoor activities.