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primary 5 | Maths
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Anyone can contribute an answer, even non-tutors.
I can't think of a solution without employing algebra. Thanks in advance.
Date Posted: 3 years ago
Views: 590
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Cost of a chair = $69 - $24 = $45
Assumption method :
Assume that there are 75 desks and 75 chairs first.
Difference in cost = 75×$69 - 75×$45
= 75 × $(69 - 45)
= 75 × $24
= $1800
(Or if you know your grouping methods, 1 desk cost $24 more than 1 chair so 75 desks cost 75 × $24 = $1800 more than 75 chairs)
But this is too high. The actual difference is only $660.
$1800 - $660 = $1140. The difference needs to be lowered by $1140.
So we need to replace some desks with chairs. For every desk removed, the difference drops by $69. Replacing it with a chair means the difference drops by another $45.
(Basically, the gap between their total costs is now narrower)
So in the replacement of 1 desk with 1 chair, the difference in price drops by : $69 + $45 = $114
$1140 ÷ $114 = 10. So we need to replace 10 desks with 10 chairs.
Number of chairs actually bought = 75 + 10 = 85
Assumption method :
Assume that there are 75 desks and 75 chairs first.
Difference in cost = 75×$69 - 75×$45
= 75 × $(69 - 45)
= 75 × $24
= $1800
(Or if you know your grouping methods, 1 desk cost $24 more than 1 chair so 75 desks cost 75 × $24 = $1800 more than 75 chairs)
But this is too high. The actual difference is only $660.
$1800 - $660 = $1140. The difference needs to be lowered by $1140.
So we need to replace some desks with chairs. For every desk removed, the difference drops by $69. Replacing it with a chair means the difference drops by another $45.
(Basically, the gap between their total costs is now narrower)
So in the replacement of 1 desk with 1 chair, the difference in price drops by : $69 + $45 = $114
$1140 ÷ $114 = 10. So we need to replace 10 desks with 10 chairs.
Number of chairs actually bought = 75 + 10 = 85
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