Re: Credit card balance transfer fee problem
- To: mathgroup at smc.vnet.net
- Subject: [mg103394] Re: [mg103184] Credit card balance transfer fee problem
- From: Kelly Jones <kelly.terry.jones at gmail.com>
- Date: Sun, 20 Sep 2009 06:20:14 -0400 (EDT)
- References: <200909101118.HAA17845@smc.vnet.net>
On 9/10/09, Kelly Jones <kelly.terry.jones at gmail.com> wrote:
>
> My credit card company loans me $10000 for a cash advance fee of 3%
> ($300), and an interest rate of 2% per year. I have to pay off the
> loan in 1 year, but my monthly minimum payment is only 3% of my
> outstanding balance. In other words, I can pay 3% of my balance for
> the first 11 months, and then pay off the remaining balance in the
> 12th month.
Thanks again to everyone who's helping.
I finally figured out that it's best to solve both equations
simultaneously:
sol = DSolve[{
have'[t] == have[t]*Log[1+invest]-monpay*owed[t],
owed'[t] == owed[t]*Log[1+interest]-monpay*owed[t],
have[0] == borrowed, owed[0] == borrowed*(1+fee)
}, {have[t], owed[t]}, t]
h[t_, borrowed_, fee_, interest_, monpay_, invest_] = have[t] /. sol[[1]]
o[t_, borrowed_, fee_, interest_, monpay_, invest_] = owed[t] /. sol[[1]]
Trying to solve what value of invest makes h() and o() equal at t=1:
Solve[h[1,borrowed,fee,interest,monpay,invest] ==
o[1,borrowed,fee,interest,monpay,invest], invest]
yields a nonsensical answer.
With arbitrary t, Mathematica can't solve it at all
Solve[h[t,borrowed,fee,interest,monpay,invest] ==
o[t,borrowed,fee,interest,monpay,invest], invest, t]
Thoughts?
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- References:
- Credit card balance transfer fee problem
- From: Kelly Jones <kelly.terry.jones@gmail.com>
- Credit card balance transfer fee problem