#### Answer

$\frac{1}{4}$

#### Work Step by Step

P(E) = $\frac{no.\ of\ outcomes\ in\ favor}{Total\ no\ of\ outcomes}$
There is a total of 52 cards, so there are 52 outcomes.
There are 13 diamonds, so there is a total of 13 favorable outcomes.
P(E) = $\frac{13}{52}$ = $\frac{1}{4}$