On a certain date, Pat invested $5,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $20,000, in how many years, the total value of the investment plus interest will increase to $30,000?  Pick one.
A) 15
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 5,000 to quadralope 12 years.   So according to the rule: 72/x is the no of years 5,000.00 took to double 10,000.00.   Again, 10,000.00 took to double 20,000.00 same (72/x) no of years.   72/x+ 72/x = 12   x = 12% (though rate here is not very much required).   Again, 20,000.00 takes the same (72/x) no of years to double 30,000.00.   72/x = 6 years.   So altogather:   5,000 - 10,000 = 6 years   10,000 - 20,000 = 6 years   20,000 - 30,000 = 3 years   15nswer 15 15 years.
<result>A</result>
On a certain date, Pat invested $5,000 at x percent annual interest, compounded annually. If the total value of the investment plus interest at the end of 12 years will be $20,000, in how many years, the total value of the investment plus interest will increase to $30,000?