Exponential growth and compound interest

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alexandria
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Homework Statement


Text problem: Adreece is saving for a down payment on a house. How much must he invest now, in one lump sum, in order to have $20 000 at the end of 5 years? Assume the annual interest rate is 6.25% compounded monthly. (5 marks)


Homework Equations


Formula P = A / (1 + i)^n, shown as typeset mathematics.


The Attempt at a Solution


here is my attempted answer, can someone please verify if my method is accurate and if my solution is correct? thanks for the help!
Worked solution in text form: present value of an investment with future value $20 000, annual rate 6.25% compounded monthly over 5 years, using P = A/(1+i)^n with i = 0.005208333 and n = 60, giving P ≈ $14598.54.
 
alexandria said:

Homework Statement


View attachment 101163

Homework Equations


View attachment 101164

The Attempt at a Solution


here is my attempted answer, can someone please verify if my method is accurate and if my solution is correct? thanks for the help!
View attachment 101165

Your method is OK, but I get $14644.18 instead of your $14598.54.

Also: do NOT use the exact same title "exponential growth and compound interest" for two different threads. When you do that it makes it harder for other readers/helpers to navigate your PF threads.
 
i think its because i didnt round 0.005208333
would my answer still be considered right, or is it better to round ??
 
alexandria said:
i think its because i didnt round 0.005208333
would my answer still be considered right, or is it better to round ??

Well, the correct answer is $14644.18, while your answer is $14598.54. Admittedly, the difference ($45.64) is not very large compared to the base values, but nevertheless one answer is not correct, no matter how you look at it.

As to rounding: I cannot answer that question because you do not specify what accuracy you round to. Generally, though, it is best to keep full calculator accuracy during your computations, and round off the answer only at the end.
 
ok got it, sorry for the late reply, but thanks for the help!