Answer: 10.1246 years (approx)
Step-by-step explanation:
Here, She invests in a CD with an annual interest rate of 6.90% compounded quarterly.
Let the initial amount or principal = P
And, Let after t years it is doubled.
Therefore, [tex]2P= P(1+\frac{6.9}{400} )^{4t}[/tex]
⇒ [tex]2 = (1+\frac{6.9}{400} )^{4t}[/tex]
⇒[tex]log 2 = t log(1+\frac{6.9}{400} )^4[/tex] ( By taking log both sides)
⇒[tex]log 2 = t log(1.01725 )^4[/tex]
⇒t= log 2/log 1.07080599536= 10.1245504311≈10.1246 years
