It's not yet ladies night!

Assuming the absence of hermaphrodites and such, there are 30 males in the club. Hence the shortage of females is $30-20=\boxed{10}$ .

It is so easy that I thought it was a catch!

$50 - 20\ = 30$ [Males]

So: $30 - 20 =\boxed{10}$

Total people in the club= 50

No. of females= 20

therefore No. of males= 30

Since females are less by males by 10

therefore 10 more ladies must be brought inside to equal the nos.

Since there are total 50 people at the club and 20 of them are females so 30 are males. The bouncer must let in 10 people (all female-we suppose this because the question contains the keyword minimum) so the number becomes equal. 30 = 30

one thing that should be noted is we aren't considering the bouncer as a part of the party.{as a male}. otherwise answer would have been 11.

Total no of people's in club 50 and the female count is 20 then remaining people are male => 50 - 20 = 30 each one of them in club, then remaning 10 people's are bouncer's

THE LEAST IS 10 SINCE THERE ARE 10 MORE MALE THAN FEMALE