Question

Caroline puts $400 into a savings account that earns 6% annually. Write a function that represents this situation, where t is the time in years. Solve algebraically after how many years she will get $1200 in her account (round it to the nearest year).

Answer 1

Answer: 19 years

Step-by-step explanation:

Given

Amount invested $\ 400$

Rate of interest $R=6\%$

after 1-year amount becomes

$A=400\left (1+6\%\right)\\A=400\left (1+0.06\right)\\A=400\times 1.06\\A=\ 424$

After n years it is

$A=400\left (1.06\right)^n$

Sum accumulated is $\ 1200$

$\Rightarrow 1200=400\left(1.06\right)^n\\\Rightarrow 3=\left(1.06\right)^n\\\text{Taking log both sides}\\\Rightarrow n=\dfrac{\ln 3}{\ln 1.06}\\\\\Rightarrow n=18.85\approx 19\ \text{years}$