why do bb need even number of housemates

[JohnnyBB]

i just dont get it why dose bb need a even number of housemates tbh we didint really need new housemates tonight but theres somthink in the back of my mind just wont go away. Why Dose BB Ned An Even Number Of Housemates???

[bigbr0ther]

I wish they could just have all 20 people enter on launch night rather than 16 on launch night and 4 later in the series.