Compound Interest: 3 Equal Ann. Repayments, $3,000 Loan, 9% Rate

  • Context: High School 
  • Thread starter Thread starter NosajW
  • Start date Start date
  • Tags Tags
    Economics
Click For Summary

Discussion Overview

The discussion revolves around calculating the breakdown of three equal annual repayments for a $3,000 loan at a 9% interest rate compounded annually. Participants explore how to determine the interest and principal components of each payment over the repayment period.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on how to approach the problem of three equal annual repayments, expressing familiarity with compound interest but confusion about the repayment structure.
  • Another participant mistakenly suggests that three payments per year are involved, which is corrected by others who clarify that there are three equal annual payments.
  • Participants discuss the calculation of interest and principal payments, with one proposing a method of calculating interest on the remaining balance after each payment.
  • Concerns are raised about the total amount paid over three years not matching the compounded loan amount, leading to questions about the annual payment structure.
  • A participant provides a detailed breakdown of calculations for each year, including the principal and interest amounts, and seeks validation of their approach.
  • Another participant agrees with the breakdown but notes that if fractions of pennies are ignored, the final balance may not be exactly zero at the end of the repayment period.

Areas of Agreement / Disagreement

Participants generally agree on the method of calculating interest and principal payments but express differing views on the implications of rounding and the total amount paid versus the compounded loan amount. The discussion remains unresolved regarding the exact handling of fractional amounts in the calculations.

Contextual Notes

Participants highlight potential issues with rounding and the treatment of small discrepancies in the final balance, indicating that these factors may affect the accuracy of the calculations.

NosajW
Messages
11
Reaction score
0
You are about to borrow $3,000 from a bank at an interest rate of 9% compounded annually. You are required to make three equal annual repayments in the amount of $1,185.16 per year, with the first repayment occurring at the end of year one. For each year, show the interest payment and principal payment.

I know how to do compound interest, but I don't get what this three equal annual repayments thing is. Can someone explain how to do this problem? Thanks in advance
 
Physics news on Phys.org
3 payments/year means that a payment is made each 4 months of 1/3rd the annual payment?
 
Last edited:
it's not three payments a year. there's a total of three equal annual payments of $1,185.16. I'm supposed to find out the interest and principal per year
 
Oh I see
Well $3,000 is the principle. 9% of $3000 is interest. Subtract the payment from their sum. Then another 9% on this number for the 2nd year interest, etc.
 
Last edited:
it says three equal payments of 1185.16 but if you multiply that by 3 you don't get 3000(1.09)^3 = 3885.09 o_O how would you do it annually instead of 3 years?
 
Crusty said:
Oh I see
Well $3,000 is the principle. 9% of $3000 is interest. Subtract the payment from their sum. Then another 9% on this number for the 2nd year interest, etc.

their sum is 1185.16*3?
 
Paying once a year, then adding interest on the remainder-
((3000*1.09-1185.16)*1.09-1185.16)*1.09-1185.16 = 0.014004 so there's some left over.
 
Last edited:
is there a formula for this? so..
year 1 = 3000*1.09 - 1185.16 = 2084.84, principal = 3000, interest = 270
year 2 = 2084.84*1.09 - 1185.16 = 1087.32, principal = 2084.84, interest = 187.64
year 3 = 1087.32*1.09 - 1185.16 = 0, principal = 1087.32, interest = 97.86

is this correct?
 
Assuming the interest is paid first and then the principle is paid down each year, then yes the new 9% each year would be all the interest.
If the fractions of pennies are kept by the loan giver or left off the equations, then there's nothing left at the end of year 3.

3000 * 1.09 - 1 185.16 = 2 084.84
2084.84 * 1.09 - 1 185.16 = 1087.3156; 1087.3156-.0056 = 1087.31
1087.31 * 1.09 - 1 185.16 = 0.0079; 0.0079-0.0079 = 0
 
  • #10
you have been very helpful, thank you crusty!
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
Replies
16
Views
6K
Replies
2
Views
11K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
7K
Replies
1
Views
1K
  • · Replies 5 ·
Replies
5
Views
10K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
3
Views
4K