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(b) Step 1: Add minutes:
34 minutes + 47 minutes = 81 minutes h min

81 minutes = 60 minutes + 21 minutes 1
= 1 hour 21 minutes ( 1 hour = 60 minutes) + 6 34
47
8
Step 2: Add hours: 15 21
1 hour + 6 hours + 8 hours = 15 hours

6 hours 34 minutes + 8 hours 47 minutes = 15 hours 21 minutes
example 2: Subtract the following:

(a) 48 minutes 34 seconds from 54 minutes 20 seconds

(b) 7 hours 54 minutes from 13 hours 22 minutes
Solution:

(a) Step 1: Subtract seconds. There are not enough seconds.
min s
So, regroup minutes and seconds.
53 80
54 minutes 20 seconds = 53 minutes 80 seconds 54 20

Now, 80 seconds – 34 seconds = 46 seconds – 48 34

Step 2: Subtract minutes: 5 46
53 minutes – 48 minutes = 5 minutes
54 minutes 20 seconds – 48 minutes 34 seconds = 5 minutes 46 seconds

(b) Step 1: Subtract minutes. There are not enough minutes.
h min
So, regroup hours and minutes 12 82
13 hours 22 minutes = 12 hours 82 minutes 13 22

Now, 82 minutes – 54 minutes = 28 minutes – 7 54
5
28
Step 2: Subtract hours: 12 hours – 7 hours = 5 hours
13 hours 22 minutes – 7 hours 54 minutes = 5 hours 28 minutes
example 3: What time will it be at 3 hours 40 minutes after 6:30 p.m.?

Solution: h min
1
Step 1: Convert 6:30 p.m. into 24-hour clock. 18 30
6:30 p.m. = 1830 hours = 18 hours 30 minutes + 3 40
Step 2: Add 3 hours 40 minutes and 18 hours 30 minutes. 22 10

Š 30 minutes + 40 minutes = 70 minutes
70 minutes = 60 minutes + 10 minutes = 1 hour + 10 minutes

Š 1 hour + 18 hours + 3 hours = 22 hours
Step 3: Required time = 22 hours 10 minutes = 2210 hours = 10:10 p.m.

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