SOLUTION: If Kevin invests $50,000 into an account that earns 6.15% interest compounded monthly, how long will it take his money to double? (round to one decimal place) A.135.6 years B.1

Question 1170821: If Kevin invests $50,000 into an account that earns 6.15% interest compounded monthly, how long will it take his money to double? (round to one decimal place)
A.135.6 years
B.11.6 years
C.11.3 years
D.9 years
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
Rule of 70 would exclude a and d. 70/6.15=11.38 favoring c
P=Po(1+(0.0615/12)^nt
2=(1.005125)^nt
ln2=nt ln 1.005125
nt=135.6 compounding times
divide by 12 to get years , which is 11.3
C
Answer by ikleyn(52872)   (Show Source): You can put this solution on YOUR website!
.

In such problems, the quantum of the time is   a MONTH.

Therefore, would the problem be formulated ACCURATELY by its composer,
it should ask about the MONTHS --- not about the decimal parts of the year.

DIAGNOSIS:   The problem formulation is   lame.

/\/\/\/\/\/\/\/

For the composer's info :

A year is 12 months - - - not 10 months.

One more notice specially related to the solution by @Boreal :

nt=135.6 compounding times CAN NOT be non-integer value. It is NECESSARY an INTEGER. It MUST be an integer.

So, the correct answer in this case is nt = 136 compounding times,
which is 136 months divided by 12 months = 11 years and 4 months.

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