The mistake is to count guests and order that many chairs. At a party with a jumper, a good share of the guest list is a child who will be in the bounce house rather than sat down, and adults circulate. What you are really seating is the peak — the moment everybody sits at once to eat.
A workable rule: seat about three quarters of the adults, plus a chair for every child under about four, and you will not run short at the table while leaving the yard walkable the rest of the time.
Against the packages, that works out roughly like this. A bounce house or slide rental comes with 2 tables and 16 chairs, which covers a small party of about twenty. The 20×20 tent package brings 4 tables and 32 chairs and a bounce house — comfortable up to about forty-five. The 20×30 package brings 6 tables and 48 chairs plus the bounce house, which is the one to book once the list runs past that.
The tent is worth more than the seating count suggests, because in this valley shade is what decides whether people stay outside at all. If the party is between about noon and five in summer, book the shade. Call (209) 589-5225 and we'll talk through what fits.