Another quick approach is as follows:
Just count the number of decimal places, and raise 2 to that power. Since there are four decimal places in this question, then the denominator is $2^4$. Then, just calculate the numerator as a binary number, in this case, $(1101)_2=(13)_{10}$
So the final number is $\frac{13}{2^4}=\frac{13}{16}=0.8125$.