Given
investment = $1200
earned in interest = $ 66
Time = one year
Find out the interest rate .
To proof
FORMULA
[tex]Simple\ interest =\frac{Principle \times Rate\times Time}{100}[/tex]
here
Principle =$ 1200
Simple interest =$66
Time = 1 year
put these value in the above formula
we get
[tex]Rate =\frac{66 \times100 }{1200}[/tex]
Rate = 5.5 %
The interest rate is 5.5 %
Hence proved