Page 131 - Start Up Mathematics_5

Example 2: Subtract 8 h 45 min from 13 h 20 min.

Solution: h min Quick Tip
7 10
12 8 0 (60 + 20 = 80) 20 is less than 45, so we
1 3 2 0 (1 h = 60 min) borrow 1 h, i.e., 60 min
– 8 4 5 from 13 hours.
4 3 5

So, 13 h 20 min – 8 h 45 min = 4 h 35 min.

Example 3: Add 4 h 20 min 15 s and 5 h 16 min 5 s.

Solution: h min s
1
4 2 0 1 5

+ 5 1 6 0 5
9 3 6 2 0

So, 4 h 20 min 15 s + 5 h 16 min 5 s = 9 h 36 min 20 s.

Example 4: Add 6 h 40 min 35 s and 3 h 25 min 45 s.

Solution: h min s Quick Tip
1 1
6 4 0 3 5 • 35 s + 45 s = 80 s which is more than 60 s.
So, subtract 60 s (i.e., 1 min) from 80 s
+ 3 2 5 4 5 and carry over 1 to minutes.

1 0 0 6 2 0
• 40 min + 25 min + 1 min
= 66 min > 60 min
So, 6 h 40 min 35 s + 3 h 25 min 45 s So, subtract 60 min (i.e., 1 hour)
= 10 h 6 min 20 s. from 66 min and carry over
1 to hours.

Example 5: Subtract 8 h 38 min 29 s from 15 h 26 min 15 s.

Solution: h min s
8 5 Quick Tip
1 4 2 5 7 5
1 5 2 6 1 5 • 15 s – 29 s is not possible. So, borrow 1

– 8 3 8 2 9 min (i.e., 60 s) from minutes and add to
15. Then subtract 29 from it.
6 4 7 4 6 • 25 min – 38 min is not possible.

So, borrow 1 h (i.e., 60 min) from
So, 15 h 26 min 15 s – 8 h 38 min hours and add to 25.
29 s = 6 h 47 min 46 s. Then subtract 38 from it.

123