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proper use of hubo and hay?
Ahora hay una fiesta de graduación en el patio de la universidad.
hubo muchos invitados en la fiesta de aniversario anoche.
Ya hubo una muerte en su familia el año pasado.
Siempre hay galletas y dulces en esas conferencias.
Hubo varias botellas de vino, pero los invitados se las tomaron.
Por las mañanas hay unos postres deliciosos en esa tienda.
2 Answers
I tend to use había for there was/were just describing a state, an existing condition or that something or someone etc was somewhere - to me hubo is more for actions, changes or specific events. So your examples seem to fall into the hubo categories - either specific events (an anniversary) an action (I guess dying/death is an action) or change - (there were bottles but they've gone now). 
Just to expand a little and offer a couple more examples - anyone please correct me if I don't quite have it right but .... I'd say the difference between había un accidente and hubo un accidente is that in the first one it's just telling you there was an accident, an accident had happened before arrived and you came across it or you're just describing it but in the second (hubo) you're saying that it happened then and there - you're walking along minding your own business and boom crash there was an accident.
Becoming really familiar the differences between the imp and pret will help you the most. Hubo the preterite is used for events that occurred only once or that or whose ending you definitely know about. Quite often you'll find it with time markers like ayer, el año pasado, etc. On the other hand había the imperfect is used to describe circumstances occuring in the past, descriptions in past etc (not to say that you wont find this with ayer etc).
Hubo the preterite is also used for simultaneous actions - fui al centro y hubo un accident, but use the imperfect if you come across a situation that was already ongoing - fui al centro y había un accidente.
I hope those ramblings help a little
Great job jmh1990
