(a) 1 hr = 60 min
2 hr = 2 × 60 = 120 min
4 hr = 4 × 60 = 240 min
7 hr = 7 × 60 = 420 min
480 min = 8 hr
As, 8 hr = 8 × 60 = 480 min
9 hr = 9 × 60 = 540 min
660 min = 11 hr
As, 11 hr = 11 × 60 = 660 min
720 min = 12 hr
As, 12 hr = 12 × 60 = 720 m
(b) Do as instructed. You can use the above double number line for the following ‘ conversions.
Solution:
(i) 1 hr 10 min = 60 min + 10 min = 70 min
So, 1 hour 10 minutes = 70 minutes.
(ii) 2 hr 45 min = 120 min + 45 min = 165 min
So, 2 hours 45 minutes = 165 minutes,
(iii) 3 hr 15 min = 3 times 60 + 15 min – 180 min + 15 min = 195 min
So, 3 hours 15 minutes = 195 minutes.
(iv) 4 hr 20 min = 4 times 60 + 20 min
= 240 min + 20 min = 260 min
So, 4 hours 20 minutes = 260 minutes.
(v) 75 min = 60 min + 15 min = 1 hr 15 min
So, 75 minutes = 1 hour 15 minutes.
(vi) 150 min = 120 min + 30 min = 2 hr 30 min
So, 150 minutes = 2 hours 30 minutes.
(vii) 220 min = 120 min + 60 min + 40 min = 2 hr + 1 hr + 40 min = 3 hr 40 min
So, 220 minutes = 3 hours 40 minutes.
(viii) 390 min = 240 min + 120 min + 30 Mn = 4 hr + 2 hr + 30 min = 6 hr + 30 min
So, 390 minutes = 6 hours 30 minutes
(c) Fill in the blanks in the double number line to complete the conversions.
Solution:
120 sec = 2 min, as 2 min = 2 × 60 = 120 sec.
Multiplying by 5 to the previous marking we get the number for the next marking on the number line for minutes. To get the corresponding seconds on the seconds number line we need to multiply the number of minutes by 60.
(i) 320 sec = 300 sec + 20 sec = 5 min + 20 sec
So, 320 sec = 5 min 20 sec
(ii) 225 sec = 120 sec + 60 sec + 45 sec
= 2 min + 1 min + 45 sec
So, 225 sec = 3 min 45 sec
(iii) 700 sec = 600 sec + 60 sec + 40 sec
= 10 min + 1 min + 40 sec
So, 700 sec = 11 min 40 sec
(iv) 1000 sec = 900 sec + 60 sec + 40 sec
= 15 min + 1 min + 40 sec
So, 1000 sec = 16 min 40 sec
(v) 10 min 13 sec = 600 sec + 13 sec
= 613 sec
So, 10 sec 13 sec = 613 sec
(vi) 4 min 8 sec = 2 min + 2 min + 8 sec
= 120 sec + 120 sec + 8 sec = 248 sec
So, 4 min 8 sec = 248 sec
(vii) 15 min 40 sec = 900 sec + 40 sec
= 940 sec
So, 15 min 40 sec = 940 sec