G1.4 16 cards are marked from 1 to 16 and one is drawn at random. If the chance of it being a perfect square number is $\frac{1}{d}$, find $d$.
Perfect square numbers are $1,4,9,16$.
$$
\begin{array}{l}
\text { Probability }=\frac{4}{16}=\frac{1}{d} \\
d=4
\end{array}
$$