Page 164 - ICSE Math 4

Subtraction of Time

To subtract me, we follow the given steps.

• Subtract the seconds. If the number of seconds to be subtracted is more than the
original seconds, then

(a) borrow 1 minute or 60 seconds from the original minutes.
(b) subtract 1 from the original minutes.

(c) increase the number of seconds by 60.

• Subtract the minutes. If the number of minutes being subtracted is more than the
original minutes, then
(a) borrow 1 hour or 60 minutes from the original hours.

(b) subtract 1 from the original number of hours.

(c) increase the number of original minutes by 60.
• Subtract the remaining hours.

Example 9: Subtract 3 hours 15 minutes 50 seconds from 8 hours 50 minutes 55 seconds.

Solu on: Step 1: Subtract the seconds fi rst.
h min s
55 s – 50 s = 5 s 4 10
8 50 55
Write 5 under the seconds column.
– 3 15 50
Step 2: Subtract the minutes.
5 35 05
50 min – 15 min = 35 min

Write 35 under the minutes column.
Step 3: Subtract the hours.

8 h – 3 h = 5 h
Write 5 under the hours column.

So, 8 h 50 min 55 s – 3 h 15 min 50 s = 5 h 35 min 5 s.

Exercise 12.4

1. Add the following.
(a) 3 h 20 min 30 s, 2 h 15 min 5 s and 3 h 45 min 50 s

(b) 8 h 20 min 55 s, 7 h 35 min 40 s and 6 h 50 min 16 s

(c) 16 h 30 min 40 s, 1 h 20 min 10 s and 3 h 45 min 15 s

(d) 6 h 45 min 25 s, 3 h 20 min 30 s and 2 h 15 min 45 s

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