Solved

Posted on 2005-04-13
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Can anyone explain how this was solved as i need to master this.. many thanks

100000 = 146400 / ( r + 1 )^ 4

r = 10

0
Question by:ProgramVB
1 Comment

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Accepted Solution

The solution to the problem is not 10....plugging in 10 to the equation I get:

100000 = 146400 / (11)^ 4
100000 = 146400 / 14641
100000 = 9.993                 <----false

So, to solve it:

100000 = 146400 / (r+1)^4

First, multiply both sides by (r+1)^4...the right side cancels and you get:

(r+1)^4 * 100000 = 146400

now, divide both sides by 100000 to get

(r+1)^4 = 1.464

Take the 4th root of both sides to get

r+1 = 1.09998

Subtract 1 from both sides:

r = .09998

And if you plug this back in you get:

100000 = 146400 / (1.09998)^4
100000 = 146400 / 1.464
100000 = 100000                     <-----true
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