Page 146 - Start Up Mathematics_4

EXERCISE 10.4

1. Convert the time in hours to minutes.
1
(a) 6 hours (b) 2 hours (c) 4 hours 20 minutes
2
(d) 3 hours 45 minutes (e) 9 hours (f) 5 hours 15 minutes
2. Convert the time in minutes to hours.

(a) 160 min (b) 250 min (c) 360 min (d) 540 min
(e) 1020 min (f) 1260 min (g) 780 min (h) 2040 min

Addition and Subtraction of Time

Given below are the steps for adding time.

1. Add the hours together. 2. Add the minutes together.
If the number of minutes is 60 or more, then

(a) subtract 60 from the number of minutes.
(b) increase the number of hours by 1.
(c) repeat this process if the number of minutes is still 60 or more.

(d) write the minutes left in the minutes column.
For example, 75 min = 75 min – 60 min = 1 h 15 min.

Example 6: Add 2 hours 15 minutes and 4 hours 35 minutes.

Solution: h min
1
2 1 5

+ 4 3 5
6 5 0

Thus, 2 h 15 min + 4 h 35 min = 6 h 50 min.

Example 7: Add 4 hours 25 minutes and 3 hours 50 minutes.

Solution: h min
4 2 5

+ 3 5 0
1 h
+ 7 7 5 is more than 60 minutes
– 6 0 (1 h)

8 1 5

Thus, 4 h 25 min + 3 h 50 min = 8 h 15 min.

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