But, you tell your client that's not good enough evidence.
You make up the following chart:

It's just chance.
The office could be 5 males or 5 females and the change of one person would make it 6 to 4. It could have just as easily been 4 males or 6 females.

Intuitively, you can see that it would be hard to convince someone that this 60 - 40 split is discrimination. It's too easy to be just luck.