Answer: The rate of interest per annum is 1.3%.
Step-by-step explanation:
Given Principal P= $1000
time period n=3
Amount A=$1040,40
To find rate of interest per annum r
We know that
[tex]A=P(1+\frac{r}{100} )^3\\\Rightarrow\ 1040=1000(1+\frac{r}{100})^3\\\Rightarrow\ 1.040=(1+\frac{r}{100})^3\\\text{taking log on both sides}\\log(1.040)=3log(1+\frac{r}{100})\\\Rightarrow0.039=3log(1+\frac{r}{100})\\\Rightarrow0.013=log(1+\frac{r}{100})\\\\\Rightarrow\ e^{0.013}=(1+\frac{r}{100})\\\Rightarrow\ 1.013=(1+\frac{r}{100})\\\Rightarrow\ \frac{r}{100}=1.013-1=0.013\\[/tex]
⇒ r = 1.3%.
