Shows are different sizes in different part of the country. In general, the ARBA guideline is for a judge to judge no more than 250 rabbits on an given day. It's quite common to assume 200-250 rabbits per judge, so if you are trying to figure out how many rabbits are in a show room, take the number of judges then multiple by 200-250, you'll the get range of "entries". Each "entry" is defined as a rabbit being judge once. If it's a double show day, then each rabbit will be judged twice. If a certain breed has a specialty show on top of the double all breed show, then the same rabbit will be counted as 3 entries.
Open and youth shows are separate, adult cannot show in the youth show but youth can show in the open show but not with the same rabbits that are entered in the youth show.