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Posted by Sean-usenet on February 9, 2007, 1:21 pm
Hi Tad
Yea, $2,236.85 is right, I understand it now. I won't make that
mistake again!
Thanks for you help!
Sean
> Sean-usenet wrote:
> > Thank so much for any help you can provide, I appreciate it!
>
> I get 2236.85.
>
> A simple way to solve it is to treat it as an ordinary annuity of 49
> months. The first month nothing happens until the final day when you
> make your first "deposit." Then, another deposit lands at the end of
> each month, for the next 48 months. And you immediately see your 140552
> at the end of month 49 (which is really just 48 months after your first
> deposit). This models the deposit pattern you laid out.
>
> So you put your calculator in END mode, N=49, PV=0, FV=148552, %I=12, 12
> PER/YR, and you get PMT=2236.85.
>
> Another, harder way is to treat it as an ordinary annuity of 48 months
> with an initial deposit (i.e., a non-zero PV). Iterate with N=48, %i=12,
> FV=140552, 12 PER/YR, "END" mode (for an ordinary annuity) and try to
> match PV and PMT. You still get 2236.85.
>
> Your mistake is equating a 48 month ordinary annuity (with an extra
> deposit at t=0) with a 49 month annuity due. Those aren't the same. The
> latter leaves the entire balance invested for an extra month after the
> end of year four. Play around with the extra 1% you get at the end of
> the pipe and you'll see what I mean.
>
> So your prof sounds right. Keep in mind that he's using the 49 month
> annuity calculation just as a shortcut to the answer. It's not that the
> money is invested 49 months, but that the deposit pattern over 48 months
> (including an initial one) is mathematically equivalent to an ordinary
> annuity of 49 months.
>
> -Tad
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