(a) Solve 25x^2 + 23x -54 = 0
(b) Andy deposited $ 25000 in a bank on his 20th birthday and another
$ 23000 on his 21st birthday. The bank offered an interest rate of r% p.a.
compounded yearly for both deposits. If he received a total amount of
$ 54000 on his 22nd birthday , find the value of r by using (a) .
Maths ( Percentage )
2011-07-15 7:13 am
回答 (1)
2011-07-15 7:37 am
✔ 最佳答案
(a)By Quadratic formula ,
圖片參考：http://upload.wikimedia.org/math/3/e/a/3ea647783b5121989cd87ca3bb558916.png
x = [-23 + square root (23^2-4*25*(-54) ] / 2a or
x = [-23 - square root (23^2-4*25*(-54) ] / 2a
x = 1.08 or -2
(b)
25000 (1+r)*(1+r) + 23000 * (1+r) = 54000
[25000 (1+r)*(1+r) + 23000 * (1+r)]/1000 = 54000/1000
25(1+r)^2 + 23(1+r) - 54 = 0
Let x = 1+r,
25x^2 + 23x -54 = 0
x = 1.08 or -2 (not possible answer)
Hence, x = 1.08
r = 0.08 or 8%
收錄日期: 2021-04-13 18:05:37
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