Class 5 Mathematics · Chapter 12

12. Racing Seconds

Solutions to all Let Us Find Out, Let Us Do and Let Us Find questions. CBSE / NCERT Class 5 Maths Mela.

Let Us Find Out

1At what time did Raghav start practising Yoga?

The minute hand is at 7 and the hour hand is between 5 and 6. He started at 5:35 a.m.

2At what time did he finish?

The minute hand is at 11 and the hour hand is just before 6. He finished at 5:55 a.m.

3How much time did he spend practising Yoga?

From 5:35 to 5:55 = 20 minutes

4Find the time elapsed between the given time periods.

(a) 01:15 p.m. to 01:42 p.m. = 27 minutes

(b) 03:18 p.m. to 08:18 p.m. = 5 hours

5The table shows the time taken by 3 children to paint a picture.

(a) Rani took the longest time (2 hours 10 minutes).

(b) Raghav took the least time (1 hour 20 minutes).

6Fill in the blanks by writing the time in the appropriate format.

12-hour format	24-hour format
05:30 a.m.	05:30 hours
08:35 a.m.	08:35 hours
11:55 a.m.	11:55 hours
02:30 p.m.	14:30 hours
05:30 p.m.	17:30 hours
09:35 p.m.	21:35 hours

For p.m. times (except 12 noon hour), add 12 to the hours to get the 24-hour format.

7Match the following.

12-hour format	24-hour format
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

School Race

1Each participant took 1 minute, but how much more? Identify the child who won the race. How much time did the child take?

1 minute = 60 seconds.

The three children took 1 min 55 sec, 1 min 56 sec and 1 min 57 sec.

The child standing at position 1 on the podium won the race. She took the least time — 1 minute 55 seconds.

The second child took 1 second more, and the third child took 2 seconds more.

Let Us Do

1Estimate whether you would take seconds or minutes to complete the following activities.

Activity	Seconds / Minutes
Blinking of eyes	Seconds
Switching on and switching off the lights	Seconds
Counting from 1–20	Seconds
Filling a glass from the tap	Seconds
Melting of an ice-cube	Minutes
Making a phone call	Minutes
Sitting down on the floor	Seconds
Drinking a glass of water	Seconds
Snapping fingers	Seconds
Washing hands	Seconds

2List events that can happen in less than a minute or in a few seconds.

Sneezing, clapping 10 times, writing my name, tying a shoelace, opening a door, jumping once, a ball falling from a table, sharpening a pencil, saying “Good morning”, closing a book.

3Estimate and verify how many of these you can do in a minute.

Activity. Use a clock with a seconds hand. Example: balloons blown — 2, push-ups — 15, breaths — 18, hops on one leg — 60. Write your own estimate first, then the actual number.

Let Us Find

1Find the number of times you can skip the rope in 10 seconds. How long does it take you to write FRIEND? To run 100 m?

Activity. Examples: about 15 skips in 10 seconds; about 5 seconds to write FRIEND; about 20 seconds to run 100 m.

Let Us Do — Observe the Clocks

1Observe the clocks and fill in the blanks.

1. Rani took 30 sec. to get out of her bed. (Seconds hand moved from 12 to 6.)

2. Raghav took 35 sec. to move from his room to the kitchen. (From 12 to 7.)

3. Ritu took 15 sec. to pick up a piece of paper from the floor. (From 9 to 12.)

4. Raghu took 60 sec. to wash his spoon and plate. (The seconds hand made a full round and the minute hand moved by 1 minute.)

Each number on the clock means 5 seconds for the seconds hand.

2Draw the missing seconds hand on the clocks on the right side.

1. 20 sec: The seconds hand starts at 12. Draw it pointing to 4.

2. 30 sec: The seconds hand starts at 12. Draw it pointing to 6.

3. 60 sec: The seconds hand starts at 9. After a full round, draw it pointing to 9 again.

4. 40 sec: The seconds hand starts at 11 (55 sec). Draw it pointing to 7 (35 sec of the next minute).

Conversion of Hours to Minutes — Let Us Do

1(a) Use the double number line to complete the conversions.

1 hr, 2 hr, 4 hr, 7 hr, 8 hr, 9 hr, 11 hr, 12 hr

60 min, 120 min, 240 min, 420 min, 480 min, 540 min, 660 min, 720 min

(b)Do as instructed.

(i) 1 hour 10 minutes = 60 + 10 = 70 minutes

(ii) 2 hours 45 minutes = 120 + 45 = 165 minutes

(iii) 3 hours 15 minutes = 180 + 15 = 195 minutes

(iv) 4 hours 20 minutes = 240 + 20 = 260 minutes

(v) 75 minutes = 1 hour 15 minutes

(vi) 150 minutes = 2 hours 30 minutes

(vii) 220 minutes = 3 hours 40 minutes

(viii) 390 minutes = 6 hours 30 minutes

(c)Fill in the blanks in the double number line and complete the conversions.

1 min, 2 min, 5 min, 10 min, 15 min, 20 min, 25 min

60 sec, 120 sec, 300 sec, 600 sec, 900 sec, 1,200 sec, 1,500 sec

(i) 320 sec = 5 min 20 sec
(ii) 225 sec = 3 min 45 sec

(iii) 700 sec = 11 min 40 sec
(iv) 1,000 sec = 16 min 40 sec

(v) 10 min 13 sec = 600 + 13 = 613 sec
(vi) 4 min 8 sec = 240 + 8 = 248 sec

(vii) 15 min 40 sec = 900 + 40 = 940 sec

2Raghav studies 4 subjects for 50 minutes each. Find the total time in hours and minutes.

4 × 50 minutes = 200 minutes = 180 + 20 = 3 hours 20 minutes

3Raghu left his house at 08:00 hours and arrived at his Nana ji’s house at 09:05 hours. How long did he take?

08:00 to 09:00 = 1 hour. 09:00 to 09:05 = 5 minutes.

He took 1 hour 5 minutes.

4Jyoti went to play at 06:15 PM. She came back after 1 hour 45 minutes. At what time did she reach home?

06:15 + 1 hour = 07:15. 07:15 + 45 minutes = 08:00 PM

5Ragini took 1 hour 10 minutes to do her homework. She finished at 09:40 PM. What time did she start?

09:40 − 1 hour = 08:40. 08:40 − 10 minutes = 08:30 PM

6Children left for a picnic at 08:30 AM and returned after 4 hours 10 minutes. At what time did they return?

08:30 + 4 hours = 12:30. 12:30 + 10 minutes = 12:40 PM

7Raji started her homework at 06:00 PM and finished in 1 hour 30 minutes. At what time did she finish?

06:00 + 1 hour 30 minutes = 07:30 PM

8Alya goes out to play at 05:30 PM and comes back after 1 hour 10 minutes. At what time does she come back?

05:30 + 1 hour 10 minutes = 06:40 PM

9The lunch break starts at 12:30 PM and ends in 35 minutes. What time will lunch end?

12:30 + 30 minutes = 01:00. 01:00 + 5 minutes = 01:05 PM

10It is 08:35 PM right now. What time will it be after 8 hours and 25 minutes?

08:35 PM + 8 hours = 04:35 AM. 04:35 + 25 minutes = 05:00 AM (the next morning)

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