Financial Lease Calculation wiz needed

Finance wiz needed: Although interest rates do not exist in leases, customers constantly ask what is the interest rate for the lease. I have a question regrading how to calculate the implied interest rate in order to get the most favorable comparison. For purposes of illustration I will use a $10,000 60 month $1 purchase option lease with 2 advance payments, a lease rate of .02345 which will yield a monthly payment of $234.50. The traditional present value method will give an implied interest rate of 15.687% using Tvalue calculator available here http://tinyurl.com/6gewp4 Recently a friend showed me another method which according to him yields an interest rate of 8.24%. He does the calculations as follows: $234.50*60=$14,124.00 Total payment $14,124.00-$10,000=$4,124.00 Total Interest Paid $4,124.00/5=$824.80 Interest Paid per Year $824.80/$10,000.00= 8.248% Interest Rate per Year Something seems weird in this calculation and I was hoping for a finance wiz to clarify the error.