On a certain date, Pat invested $10,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $40,000, in how many years, the total value of the investment plus interest will increase to $240,000?  Choose the correct choice from the following:
A) 27 B) 16 C) 18 D) 20 E) 24
if i were to choose during the test, would go for 18 or 20. probably 18 cuz it wont take too long to get the value doubled....   I found a method: Rule of 72.   Given an x% return, it takes 10,000 to quadralope 12 years.   So according to the rule: 72/x is the no of years 10,000.00 took to double 20,000.00.   Again, 20,000.00 took to double 40,000.00 same (72/x) no of years.   72/x+ 72/x = 12   x = 12% (though rate here is not very much required).   Again, 40,000.00 takes the same (72/x) no of years to double 240,000.00.   72/x = 6 years.   So altogather:   10,000 - 20,000 = 6 years   20,000 - 40,000 = 6 years   40,000 - 80,000 = 6 years   80,000 - 160,000 = 6 years   160,000 - 240,000 = 3 years   total 27 years.   27nswer 27
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On a certain date, Pat invested $10,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $40,000, in how many years, the total value of the investment plus interest will increase to $240,000?