Answer:
D. 1980.
Step-by-step explanation:
We have been given that on January 1, 1970, Lois deposited $1950 into a savings account paying 6.6% interest, compounded semiannually. We are asked to find the year in which Lois's balance hit $3900, according to the rule of 72.
The rule of 72 states the number of years it will take an investment to be double.
Since $3900 is twice the amount $1950, so we will divide 72 by our given interest rate to find the number of years it will take to double the given amount.
[tex]\text{Time it will take to double the given amount}=\frac{72}{6.6}[/tex]
[tex]\text{Time it will take to double the given amount}=10.909090\approx 11[/tex]
Since the amount will be double in 11th year, so 11th year after January 1, 1970 will be 1980.
Therefore, in year 1980 Lois amount will be double and option D is the correct choice.
