Last week, Miss Wong bought some rubbers form a shop for $140. This
week, the shop reduced the price of each rubber by $0.4. If Miss Wong
bought the rubbers this week, she could buy 5 more rubbers by paying $4
more. How many tubbers did Miss Wong buy last week?
SS1 Maths quadratic equations
2010-05-02 8:43 pm
回答 (2)
2010-05-02 9:00 pm
✔ 最佳答案
Let x rubbers did Miss Wong buy last week :Last week price of each rubber = 140/x ,
This week price of each rubber = (140 + 4) / (x + 5)
Then
(140/x) - (140 + 4) / (x + 5) = 0.4
140(x+5)/x - 144 = 0.4(x+5)
140x + 700 - 144x = 0.4x^2 + 2x
0.4x^2 + 6x - 700 = 0
x^2 + 15x - 1750 = 0
(x - 35)(x + 50) = 0
x = 35 or x = - 50 (rejected)
Miss Wong bought 35 rubbers last week.
2010-05-02 9:38 pm
Let the no. of rubbers Miss Wong bought last week be x
140 / x = 144 / (x+5) + 0.4
140 /x - 144 / (x+5) = 0.4
(-4x + 700) / [x(x+5)] = 2/5
2x^2 + 10x = -20x + 3500
2x^2 + 30x - 3500 = 0
x = 35 or -50 (rejected)
Therefore, Miss Wong bought 35 rubbers last week.
140 / x = 144 / (x+5) + 0.4
140 /x - 144 / (x+5) = 0.4
(-4x + 700) / [x(x+5)] = 2/5
2x^2 + 10x = -20x + 3500
2x^2 + 30x - 3500 = 0
x = 35 or -50 (rejected)
Therefore, Miss Wong bought 35 rubbers last week.
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