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b. Step 1. Add seconds: 48 + 56 = 104 s = (60 + 44) s

= 60 s + 44 s = 1 min 44 s
Step 2. Add minutes: 1 + 26 + 13 = 40 min

Thus, 26 minutes 48 seconds + 13 minutes 56 seconds
= 40 minutes 44 seconds.

example 2. Subtract:

a. 7 hours 54 minutes from 12 hours 22 minutes

b. 34 minutes 45 seconds from 42 minutes 10 seconds
Solution.

a. Step 1. Subtract minutes. There are not enough minutes.

So, regroup hours and minutes,
12 h 22 min = 11 h + 1 h + 22 min

= 11 h + 60 min + 22 min = 11 h 82 min

Now, 82 – 54 = 28 min.

Step 2. Subtract hours: 11 – 7 = 4 h

Thus, 12 hours 22 minutes - 7 hours 54 minutes = 4 hours 28 minutes.
b. Step 1. Subtract seconds. There are not enough seconds.

So, regroup minutes and seconds.

42 min 10 s = 41 min + 1 min + 10 s
= 41 min + 60 s + 10 s = 41 min 70 s

Now, 70 s – 45 s = 25 s.
Step 2. Subtract minutes: 41 min – 34 min = 7 min

Thus, 42 minutes 10 seconds - 34 minutes 45 seconds = 7 minutes 25 seconds.

example 3. What time will it be 3 hours 40 minutes after 6:30 p.m.?

Solution.
Step 1. Convert 6:30 p.m. to the 24-hour clock format.

6:30 p.m. = 18:30 hours = 18 hours 30 minutes

Step 2. Add 3 hours 40 minutes and 18 hours 30 minutes.

• 30 min + 40 min = 70 min

70 min = 60 min + 10 min = 1 h + 10 min
• 1 + 18 + 3 = 22 h

228 Mathematics 5