Solution:
The probability of an event is expressed as
[tex]P(event)=\frac{number\text{ of desired outcome}}{number\text{ of possible outcome}}[/tex]In a pack of 52 cards, we have
[tex]\begin{gathered} number\text{ of diamonds=13} \\ number\text{ of ace= 1} \end{gathered}[/tex]Thus, we have the probability to be evaluated as
[tex]P(ace)=\frac{1}{13}[/tex]