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Formula to figure out loan payments:

Let:
 L = loan amount
 I = yearly interest rate
 N = number of months payments
 n = number of payments per year
 P = payment
 Y = I/n/100 monthly interest rate
 Q = (1 + Y)^N

 P = -(L*Y*Q)/(1-Q)

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Formula to figure out total interest paid:

Let:
 N = number of payments
 P = payment
 L = loan amount
 i = total interest paid

 i = (NxP)-L

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