Given that Cameron has a 21% annual interest rate on his credit card, his monthly interest rate is given by:
[tex]i= \frac{\left(1+\frac{0.21}{12})^{12}-1}{12} \\ \\ =\frac{\left(1+0.0175)^{12}-1}{12} \\ \\ =\frac{\left(1.0175)^{12}-1}{12} =\frac{1.231439-1}{12} \\ \\ = \frac{0.231439}{12} =0.019287\approx\bold{1.93\%} [/tex]
