9. Your best friend has arranged to borrow $4000 from you. The deal is that the money is to be paid back in five year's time. She has agreed to pay you $850/ year, with payments due at the end of each year. The question, then, is this: What interest rate have you implicitly agreed to? 10. Starting this year-in fact, starting today-you plan to start saving money for cosmetic surgery (a new head to put on your shoulders). You'll be putting $2500 per year into an investment that is expected to earn 8% per annum. If you do this, how much can you expect to have upon making the eighth deposit? 11. You've been hired as a bookkeeper for a non-profit environmental organization. The books are a mess! Thankfully, the payables appear to be under control, but some of the loans are confusing. For instance, a wealthy donor has provided quite a number of contributions, but also a loan. The organization received $150,000 loan from this person in 2001 , at an interest rate of 4% interest. No annual interest payments are to be paid on it - when it comes due it's simply to be paid back as a single lump sum of $400,000. Okay... sounds good, but when is this loan coming due? Is it still an active loan, or has it been paid off already? You're baffled, and so you sit down to do the math to try to figure out how many years the loan must have been made for