Answer
$P(A~flush)=\frac{33}{16660}\approx0.001981$
Work Step by Step
The events "five clubs", "five diamonds", "five hearts" and "five spades" are mutually exclusive (disjoint events). Also:
$P(Five~clubs)=P(Five~diamonds)=P(Five~hearts)=P(Five~spades)=\frac{33}{66640}$
Now, using the Addition Rule for Disjoint Events (page 270):
$P(A~flush)=P(Five~clubs)+P(Five~diamonds)+P(Five~hearts)+P(Five~spades)=\frac{33}{66640}+\frac{33}{66640}+\frac{33}{66640}+\frac{33}{66640}=\frac{132}{66640}=\frac{33}{16660}\approx0.001981$
