Page 38 - ICSE Math 7

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Example 18: There are four boxes in a truck. The weights of three boxes are 8 kg, 2 kg and
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4
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5 kg. If the weight of one of these three boxes is increased by 4 kg, the total weight
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of all the four boxes becomes 30 kg. Find the weight of the fourth box.
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Solution: Weight of three boxes = 8 + 2 + 5 1 kg = 35 + 17 + 21 kg
4 8 4 4 8 4
70 + 17 + 42 129
= kg = kg
8 8
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Weight of boxes after increasing 4 kg =   129 + 4 3   kg =   129 + 35   kg
8  8 8   8 8 

= 129 + 35 kg
8
164 1
= 8 kg = 20 kg
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Total weight of four boxes = 30 kg

 1   41  60 – 41
\ Weight of the fourth box = 30 20−   kg =  30 –  kg =   kg
 2   2   2 
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= 19 kg = 9 kg
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Example 19: Sia’s monthly salary is ` 36,000. She spends of the salary on transportation, of the
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remaining salary on food and deposits of the remaining salary in a bank. Find:
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(a) the amount of money saved by Sia.
(b) Sia’s total expenditure (including money spent on transportation and food).
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Solution: (a) Money spend on transportation = of ` 36,000 = × ` 36,000 = ` 21,600
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Part of the salary remaining after spending on transportation = 1 – = 2
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\ Part of the salary spent on food = of = 1 × 2 = 1
4 5 2 4 5 10
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Part of the salary remaining after spending on food = – 10 = 10
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1 3 1 3 3
\ Part of the salary saved = of = × =
2 10 2 10 20
\ Money saved = 3 of ` 36,000 = 3 × ` 36,000 = ` 5,400
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(b) Total expenditure = Money spent on transportation + Money spent on food
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= of ` 36,000 + of ` 36,000
5 10
3 1
= × ` 36,000 + × ` 36,000
5 10
 3 1 
=  +  × ` 36,000
 5 10 

= 6 + 1 × ` 36,000 = 7 × ` 36,000 = ` 25,200
10 10

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