a math question w/ answer discussion

gmat2000 · 发表于 2011-3-24 09:54:38

If $1,000 is deposited in a certain bank account and remains in the account along with any accumulated interest, the dollar amount of interest, I , earned by the deposit in the first n years is given by the formula I =1000〔(1 +r/100 )^n - 1〕 , where r percent is the annual interest rate paid by the bank. Is the annual interest rate paid by the bank greater than 8 percent?

(1) The deposit earns a total of $210 in interest in the first two years.
(2) ( 1 +r/100 )^2 > 1.15
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【答案】A

For (1), got 210 = 1000 [ (1+2/100)^2-1]
=> 0.21= r/50+r^2/10000

but how to get r from this?... xie le!

nakadai · 发表于 2011-3-24 10:02:08

0.21=(1+r/100)^2+1
1.1=1+r/100
r=10

nakadai · 发表于 2011-3-24 10:02:48

打错了
第一行最右边的是-1

gmat2000 · 发表于 2011-3-24 12:31:55

XIE!

a math question w/ answer discussion

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