## Precalculus (6th Edition) Blitzer

a. $87,025$ dollars. b. $63,025$ dollars.
a. Given $P=50, r=0.055, t=65-25=40, n=12$ we use the annuity formula: $A=\frac{P[(1+\frac{r}{n})^{nt}-1]}{\frac{r}{n}}=\frac{50[(1+\frac{0.055}{12})^{12(40)}-1]}{\frac{0.055}{12}}\approx87,025$ dollars. b. The amount of interest earned is the difference between the final amount and the total investment. Thus, we have $I=87,025-50(12)(40)=63,025$ dollars.