How to do this problem?

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1 Answer
Oct 15, 2017

Time to double = 9.23 years
Amount after 10 years = $4,238.55

Explanation:

Compound interest C I, Amount A,
Principal P, Rate of Interest R in %, Number of years N.
A=P(1+(R/100))^N
For the amount to get doubled of Principal,
4000=2000(1+(7.8/100))^N
(107.8/100)^N=2
N.log(1.078)=log(2)
N=log(2)/log(1.078)=9.23 years

Amount after 10 years,
A=2000*(1+(7.8/100))^10
A=2000*(1.078)^10=2000*2.1193=$4,238.55