We know that there are 9 red cards, 4 blue cards, and 7 gold cards. The total number of cards is 20.
It is important to know that probability is the quotient between the number of events and the total number of possible outcomes, which in this case is 20.
The probability of picking a blue car would be
[tex]P_{\text{blue}}=\frac{4}{20}=\frac{1}{5}=0.2[/tex]