Page 132 - Start Up Mathematics_5

Example 6: Multiply 3 h 14 min 9 s by 8.
Remember
Solution: h min s

3 1 4 0 9 To multiply time, first
× 8 multiply seconds, then
minutes and finally hours.
2 4 1 1 2 7 2

Product = 24 h + 112 min + 72 s
= 24 h + 112 min + (60 + 12) s
= 24 h + 112 min + 60 s + 12 s

= 24 h + (112 min + 1 min) + 12 s (Since, 60 s = 1 min)

= 24 h + 113 min + 12 s
= 24 h + (60 + 53) min + 12 s
= 24 h + 60 min + 53 min + 12 s

= (24 h + 1 h) + 53 min + 12 s (Since, 60 min = 1 h)

= 25 h + 53 min + 12 s
Thus, 24 h 112 min 72 s = 25 h 53 min 12 s.

Alternate Method

h min s
3 1 4 0 9

× 8

2 4 1 1 2 7 2
+ 1 + 1 – 6 0
2 5 1 1 3 1 2
– 6 0

5 3

So, 3 h 14 min 9 s × 8 = 25 h 53 min 12 s.

EXERCISE 9.1

1. Add.

(a) h min (b) h min (c) h min s
9 3 0 1 2 5 0 7 1 8 2 5
+ 6 2 5 + 8 4 6 + 5 4 2 3 6

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