If Rich truely borrowed that million for only 7 days and say the balance as quoted by you each quarter was the average balance for that quarter you end up with $464k average outstanding balance. (weighted average). then used a more appropriate interest rate like 8% you would end up with about $46K in interest. However, Rich would most likely opt for the IRS's minimum blended rate of about 6%, which would yield about $38k in interest.
This point of interest and paying back the last balance of approximately $300k makes sense.
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