F4 Maths
2010-07-20 6:54 pm
The value of a car last year is r% that of two years ago, and the present value of it is (r-5)% that of last year. If the present value is 68% that of two years ago, find the value of r.
回答 (1)
2010-07-20 7:08 pm
✔ 最佳答案
Let value of car 2 years ago = Vvalue of car last year = 0.01rV
present value of car = (0.01rV)(r - 5)/100 = 0.68V
(0.01rV)(r - 5) = 68V
0.01r(r - 5) = 68
r(r - 5) = 6800
r^2 - 5r - 6800 = 0
(r + 80)(r - 85) = 0
r = -80 (rej.) or 85.
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