Question 1
At what time did Raghav start practising yoga?
Steps only
The minute hand points to 7, or 35 minutes past the hour.
The hour hand is between 5 and 6.
Answer
5:35 a.m.
CLASS 5 · MATHS MELA · CHAPTER 12
Racing Seconds
Read clocks, compare durations, use seconds, convert time units and solve start-time, end-time and elapsed-time problems.
51 worked answersAll 4 exercise setsAll 10 end-of-chapter questions
What you will learn
- Read 12-hour and 24-hour time.
- Measure short events in seconds.
- Convert hours, minutes and seconds and solve time problems.
51 worked answers · short steps first, explanations when you need them
Reading, Comparing and Writing Time
Textbook pages 155–156
Question 2
At what time did Raghav finish practising yoga?
Steps only
The minute hand points to 11, or 55 minutes.
The hour hand is almost at 6, so the hour is still 5.
Answer
5:55 a.m.
Question 3
How much time did Raghav spend practising yoga?
Steps only
From 5:35 a.m. to 5:55 a.m. is 55−35=20 minutes.
Answer
20 minutes.
Question 4(a)
Find the time elapsed from 1:15 p.m. to 1:42 p.m.
Steps only
42−15=27.
Answer
27 minutes.
Question 4(b)
Find the time elapsed from 3:18 p.m. to 8:18 p.m.
Steps only
The minute readings are equal.
8−3=5 hours.
Answer
5 hours.
Question 4(c)
Find the time elapsed from 9:15 a.m. to 11:30 a.m.
Steps only
9:15 to 11:15 is 2 hours.
11:15 to 11:30 is 15 minutes.
Answer
2 hours 15 minutes.
Question 5(a)
Raghav took 1 h 20 min, Rani 2 h 10 min and Ritu 1 h 35 min. Who took the longest?
Steps only
Rani is the only child whose time is more than 2 hours.
Answer
Rani.
Question 5(b)
Who took the least time to paint the picture?
Steps only
Both Raghav and Ritu took 1 hour.
20 minutes is less than 35 minutes.
Answer
Raghav.
Question 6
Complete the four missing entries in the time-format table.
Steps only
08:35 is before noon, so it is 8:35 a.m.
11:55 a.m. stays 11:55.
For p.m. times after 12 noon, add 12 to the hour: 5+12=17 and 9+12=21.
Answer
08:35 hours = 8:35 a.m.; 11:55 a.m. = 11:55 hours; 5:30 p.m. = 17:30 hours; 9:35 p.m. = 21:35 hours.
Question 7
Match each 12-hour time to its 24-hour form.
Steps only
Keep a.m. hours unchanged and write a leading zero when needed.
Add 12 to each p.m. hour.
Answer
6:30 a.m.→06:30; 8:45 p.m.→20:45; 11:45 p.m.→23:45; 4:30 a.m.→04:30; 7:30 p.m.→19:30; 1:30 a.m.→01:30.
Seconds in Daily Life
Textbook pages 156–158
Question Race winner
Akira, Sunita and Mary finish in 1:56, 1:55 and 1:57. Who wins and how long does she take?
Steps only
The smallest finishing time is 1 minute 55 seconds.
The picture places Sunita first with this time.
Answer
Sunita wins in 1 minute 55 seconds.
Question Seconds or minutes
Would the listed everyday activities usually take seconds or minutes?
Steps only
Use seconds for blinking, switching lights, counting 1–20, filling a glass, sitting down, drinking water and snapping fingers.
Use minutes for melting an ice cube, making a phone call and washing hands.
Answer
Seconds: blinking, switching lights, counting 1–20, filling a glass, sitting down, drinking water, snapping fingers. Minutes: melting an ice cube, making a phone call, washing hands.
Question Own events
List events that happen in less than a minute.
Steps only
Possible examples are tying a shoelace, opening a door, writing one word, clapping ten times and pouring water into a cup.
Answer
Answers vary; each sensible example should normally finish within 60 seconds.
Question One-minute table
Estimate, then measure, how many balloons, push-ups, breaths and one-leg hops you can do in one minute.
Steps only
Write an estimate before starting.
Use a timer for exactly 60 seconds and record the actual count.
Find the difference to see how close the estimate was.
Answer
Activity answer; the counts depend on the student. Record both estimated and actual numbers.
Question Let Us Find 1
How many times can you skip a rope in 10 seconds?
Steps only
Start a 10-second timer.
Count only completed skips before it ends.
Answer
Activity answer; record your measured number of skips.
Question Let Us Find 2
How long does it take you to write the word FRIEND?
Steps only
Start a stopwatch as you begin writing.
Stop it after the final letter and record the seconds.
Answer
Activity answer; record the measured time in seconds.
Question Let Us Find 3
How long does it take you to run 100 m?
Steps only
Use a measured 100 m course.
Start timing at the start signal and stop at the finish line.
Answer
Activity answer; record the measured time in seconds.
Reading and Drawing Seconds Hands
Textbook pages 159–160
Question Clock 1
How many seconds did Rani take to get out of bed?
Steps only
The seconds hand moves from 12 to 6.
That is 6 intervals of 5 seconds: 6×5=30.
Answer
30 seconds.
Question Clock 2
How many seconds did Raghav take to reach the kitchen?
Steps only
The seconds hand moves from 12 to 7.
7×5=35.
Answer
35 seconds.
Question Clock 3
How many seconds did Ritu take to pick up the paper?
Steps only
The seconds hand moves clockwise from 9 to 12.
Three intervals×5 seconds=15 seconds.
Answer
15 seconds.
Question Clock 4
How many seconds did Raghu take to wash his spoon and plate?
Steps only
The seconds hand completes one full turn and returns to 5.
One full turn is 60 seconds.
Answer
60 seconds.
Question Missing hand 1
Where should the seconds hand point after 20 seconds?
Steps only
20÷5=4.
Answer
Point it at 4.
Question Missing hand 2
Where should the seconds hand point after 30 seconds?
Steps only
30÷5=6.
Answer
Point it at 6.
Question Missing hand 3
Where should the seconds hand point after 60 seconds?
Steps only
A 60-second turn ends where it began.
Answer
Point it at 12 after one full turn.
Question Missing hand 4
Where should the seconds hand point after 40 seconds?
Steps only
40÷5=8.
Answer
Point it at 8.
Converting and Calculating Time
Textbook pages 161–163
Question 1(a)
Complete the hours-to-minutes double number line.
Steps only
Multiply each hour value by 60.
Answer
1, 2, 4, 7, 8, 9, 11, 12 hours correspond to 60, 120, 240, 420, 480, 540, 660, 720 minutes.
Question 1(b)(i)
Convert 1 h 10 min.
Steps only
60+10=70.
Answer
70 minutes.
Question 1(b)(ii)
Convert 2 h 45 min.
Steps only
2×60+45=165.
Answer
165 minutes.
Question 1(b)(iii)
Convert 3 h 15 min.
Steps only
3×60+15=195.
Answer
195 minutes.
Question 1(b)(iv)
Convert 4 h 20 min.
Steps only
4×60+20=260.
Answer
260 minutes.
Question 1(b)(v)
Convert 75 min.
Steps only
75=60+15.
Answer
1 hour 15 minutes.
Question 1(b)(vi)
Convert 150 min.
Steps only
150=2×60+30.
Answer
2 hours 30 minutes.
Question 1(b)(vii)
Convert 220 min.
Steps only
220=3×60+40.
Answer
3 hours 40 minutes.
Question 1(b)(viii)
Convert 390 min.
Steps only
390=6×60+30.
Answer
6 hours 30 minutes.
Question 1(c) line
Complete the minutes-to-seconds double number line.
Steps only
Multiply each minute value by 60.
Answer
1, 2, 5, 10, 15, 20, 25 minutes correspond to 60, 120, 300, 600, 900, 1,200, 1,500 seconds.
Question 1(c)(i)
Convert 320 seconds.
Steps only
320=5×60+20.
Answer
5 minutes 20 seconds.
Question 1(c)(ii)
Convert 225 seconds.
Steps only
225=3×60+45.
Answer
3 minutes 45 seconds.
Question 1(c)(iii)
Convert 700 seconds.
Steps only
700=11×60+40.
Answer
11 minutes 40 seconds.
Question 1(c)(iv)
Convert 1,000 seconds.
Steps only
1,000=16×60+40.
Answer
16 minutes 40 seconds.
Question 1(c)(v)
Convert 10 minutes 13 seconds.
Steps only
10×60+13=613.
Answer
613 seconds.
Question 1(c)(vi)
Convert 4 minutes 8 seconds.
Steps only
4×60+8=248.
Answer
248 seconds.
Question 1(c)(vii)
Convert 15 minutes 40 seconds.
Steps only
15×60+40=940.
Answer
940 seconds.
Question 2
Raghav studies four subjects for 50 minutes each. Find the total time.
Steps only
4×50=200 minutes.
200=3×60+20.
Answer
3 hours 20 minutes.
Question 3
Raghu travels from 08:00 to 09:05. How long does he take?
Steps only
08:00 to 09:00 is 1 hour.
09:00 to 09:05 is 5 minutes.
Answer
1 hour 5 minutes.
Question 4
Jyoti starts playing at 6:15 p.m. and plays for 1 hour 45 minutes. When does she reach home?
Steps only
6:15 p.m.+1 hour=7:15 p.m.
7:15 p.m.+45 minutes=8:00 p.m.
Answer
8:00 p.m.
Question 5
Ragini finishes homework at 9:40 p.m. after 1 hour 10 minutes. When did she start?
Steps only
9:40 p.m.−1 hour=8:40 p.m.
8:40 p.m.−10 minutes=8:30 p.m.
Answer
8:30 p.m.
Question 6
A picnic starts at 8:30 a.m. and lasts 4 hours 10 minutes. When do the children return?
Steps only
8:30 a.m.+4 hours=12:30 p.m.
12:30 p.m.+10 minutes=12:40 p.m.
Answer
12:40 p.m.
Question 7
Raji starts homework at 6:00 p.m. and works for 1 hour 30 minutes. When does she finish?
Steps only
6:00 p.m.+1 hour=7:00 p.m.
7:00 p.m.+30 minutes=7:30 p.m.
Answer
7:30 p.m.
Question 8
Alya goes out at 5:30 p.m. and returns after 1 hour 10 minutes. When does she return?
Steps only
5:30 p.m.+1 hour=6:30 p.m.
6:30 p.m.+10 minutes=6:40 p.m.
Answer
6:40 p.m.
Question 9
Lunch begins at 12:30 p.m. and lasts 35 minutes. When does it end?
Steps only
12:30 p.m.+30 minutes=1:00 p.m.
Add the remaining 5 minutes.
Answer
1:05 p.m.
Question 10
It is 8:35 p.m. What time will it be after 8 hours 25 minutes?
Steps only
8:35 p.m.+3 hours 25 minutes=12:00 midnight.
Five hours remain, so move to 5:00 a.m.
Answer
5:00 a.m. the next day.