On Feb 8, 2008 3:01 PM, Ruby Quiz <james / grayproductions.net> wrote:
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> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>
> by Harrison Reiser
>
> Internal Rate of Return (IRR 
> http://en.wikipedia.org/wiki/Internal_rate_of_return) is a common financial
> metric, used by investment firms to predict the profitability of a company or
> project. Finding the IRR of a company amounts to solving for it in the equation
> for Net Present Value (NPV ¥£C http://en.wikipedia.org/wiki/Net_present_value),
> another valuable decision-making metric:
>
>                N      C_t
>         NPV =  ¥ò¥¤  ------------
>               t=0 (1 + IRR)**t
>
> This week's quiz is to calculate the IRR for any given variable-length list of
> numbers, which represent yearly cash flows, the C_t's in the formula above: C_0,
> C_1, etc. (C_0 is typically a negative value, corresponding to the initial
> investment into the project.) From the example in the Wikipedia article
> (http://en.wikipedia.org/wiki/Internal_rate_of_return), for instance, you should
> be able to produce a rate of 17.09% (to four decimal places, let's say) from
> this or a similar command:
>
>         irr([-100,+30,+35,+40,+45])
>         => 0.1709...
>
> Keep in mind that an IRR greater than 100% is possible. Extra credit if you can
> also correctly handle input that produces negative rates, disregarding the fact
> that they make no sense.
>
>
This must be a strange moment for you or maybe it is too early to say
THANK YOU FOR ALL THE FISH ;), as you still have a summary to do, but
I feel very strange by reading the "last Ruby Quiz".

Robert


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Whereof one cannot speak, thereof one must be silent.
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