SOLUTION: How much money should you deposit into a certificate of deposit that pays 4 % a year compounded continuously to have $70,000 in the account in 18 years?

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Question 1071618: How much money should you deposit into a certificate of deposit that pays 4 % a year compounded continuously to have $70,000 in the account in 18 years?
Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!

A good formula to know for discrete compounding (i.e. annually, quarterly, monthly, daily):
+F+=+P%281%2Br%2Fn%29%5Ent+
where
F=future value
P=present value
r=annual interest rate (expressed as a decimal)
n=number of compounding periods per year
t=number of years

But for continuous compounding, we need to let n%97%3E%28infinity%29, and that formula becomes:
+F=Pe%5Ert+
[ This comes from Lim n—>infinity%29 %28%281%2B1%2Fn%29%5En%29+=+e+, by making the substitution in the discrete compounding formula above of m=n/r you get n=rm and you can see the 'e' part of the limit, raised to the rt power. ]
In this problem, F=70000 and we want to know P:
+70000+=+Pe%5E%28%280.04%29%2818%29%29+
+70000+=+Pe%5E0.72+
+70000++=+P%2A%282.0544%29+
++P+=+70000%2F2.0544+
+highlight%28P=34072.66%29+ dollars