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Intern
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An investment of d dollars at k percent simple annual [#permalink]
 20 Apr 2007, 20:05
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An investment of d dollars at k percent simple annual interest yields $600 over a 2 year period. In terms of d, what dollar amount invested at the same rate will yield 2,400 interest over a 3 year period?
a. 2d/4
b. 3d/4
c. 4d/3
d. 3d/2
e. 8d/3
how do you set up the equation? I can solve by plugging in numbers but am curious to see the actual work.
tia.
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Manager
Joined: 11 Nov 2006
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(E)
Interest earned in 2 years ($600):
Interest = Principal * rate * period
600 = d * r * 2
--> r = 300/d
Interest earned in 3 years ($2400) at the same interest rate (r=300/d):
Interest = Principal * rate * period
2400 = P * (300/d) * 3
--> P = (8d/3)
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VP
Joined: 08 Jun 2005
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hi
k = intrest = k/100
d = old amount
n = new amount
2(d*k/100) = 600
d*k/100 = 300
k/100 = 300/d (constent)
3(n*300/d) = 2400
n*300/d = 800
n = 800d/300
n = 8d/3
the answer is (e) - but as you pointed out - plugging in will be much more faster considering k is constant.
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