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Homework Help: Extracting DE question

  1. Mar 14, 2010 #1
    1. The problem statement, all variables and given/known data

    A recent graduate borrowed 19000$ at an annual rate of 5%
    to buy a car from a bank. Suppose that it has made an arrangement to pay the bank
    r $ per month. Let S(t), measured in $, be the balance due on the loan at ant time
    t, measured in years.

    Write a differential equation to calculate the amount of loan left to be

    2. Relevant equations


    3. The attempt at a solution

    [tex]\frac{dS}{dt}[/tex] = [tex]\frac{S}{20}[/tex] - 12k

    i think this is wrong because something is wrong when i do an explicite solution of S

    e[tex]\frac{-t}{20}[/tex]S = 12k(1-e[tex]\frac{-t}{20}[/tex]) + 19000

    defenitely something is wrong,

    can someone help me how to translate or give some clue the question to

    [tex]\frac{dS}{dt}[/tex] form,
  2. jcsd
  3. Mar 14, 2010 #2
    FYI, its e-t/20, sorry
  4. Mar 14, 2010 #3
    i've been told that.. bank usually are compound interest.... i dont know what that means
  5. Mar 15, 2010 #4
    looks like you have to submit the answer tomorrow, ait?

    your answer should :
    monthly repayments : RM 754.85
    total interest payable : RM5290.92

    loan amount = RM 40,000
    interest rate = 5%
    loan term = 5 yrs
    repayments = monthly
    repayments type = principal & interest

    based on this calculator : http://www.banks.com.au/tools/calculator/loan-repayments/

    come on BAGINDA, think faster.... huhuhuhu
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