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.kbf?
Registered User regular

I'm having a lot of trouble with this problem and I lost my notes from the day we did interest rates

After charging $5000 to his credit card which carries a yearly interest of 20%, Bob decides to stop using his

card and to pay back $100 every month. Determine how long Bob will need to pay of his debt and how much

interest will he end up paying?

How do I set this up?

dp/dt = .2p-5000?

After charging $5000 to his credit card which carries a yearly interest of 20%, Bob decides to stop using his

card and to pay back $100 every month. Determine how long Bob will need to pay of his debt and how much

interest will he end up paying?

How do I set this up?

dp/dt = .2p-5000?

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## Posts

I was told there would be no math.

2868onbuy warhams

I was

alsotold there would be no math.vonPoonBurGeronPracticalProblemSolveronI'm not just trying to plug and chug to get the interest. I need to set up and solve a differential equation.

.kbf?onsince you seem to have the equation but can't figure it out, can't you ask your study group anyway?

the .2p-5000 should be I * P, where I = interest rate and P = principal, so it would be .2 * 5000

PracticalProblemSolveronWhat exactly is your problem? If you don't like me or my question you are more then welcome to not post in my thread.

.kbf?on.kbf?:

What does the principal change by each year?

Also, does the question say continuously compounding interest or is it just unrealistic interest that's compounded yearly?

enlightenedbumonPracticalProblemSolveronajoke. Let's all be friends.I'm in here to learn.

I have such a phobia of math, and big debt. Christ, is this problem about me?

As for the variant principal, and I'm bad at math here, how much of the 100 dollars is going to interest monthly? The 20 percent applies to his balance forward.

I'm so fucking lost. But intrigued. It's like watching university challenge.

2868onbuy warhams

So every year the new principal would be P + .2(P) - 1200? Where P is the previous total.

.kbf?onI'm mad at you because I asked a question I can't understand and you essentially told me to fuck off. And not just once. Twice.

.kbf?onWell, what's the

change, as that's dp/dt. Also, think about when the interest is calculated. Also, double check with a TA/prof about how it's being compounded. Much easier question if it's simply yearly.enlightenedbumonPracticalProblemSolveronL = P ( r + r / ((1+r)^t - 1))

(That looks like a crappy form of the equation to me - my actuarial memories tell me that there should be a simpler form of that, but that was the first google).

So, you need to rearrange that equation to solve for t.

Note also that you'll need to change either your payment amount (L) or your interest rate depending on how often it is compounded. Is your 20% a nominal or effective interest rate?

soxboxonI made an Online Tool for playing D&D- - - - - - -D&D Characters:Lyedyn Soan (Vale of Buried Shadows)Play with me on Steam

This is a rate of change problem.

Fuzzy Cumulonimbus CloudonAgain, he needs a differential equation. So he needs to think about the change in principal over time. Which he was pretty close to when last he posted but forgot something.

enlightenedbumon