Student or Learner
Here is an anouncement sample:
“The party will start at 10.00 pm.”
My book says: ‘Will' is used here instead of ‘going to' for a formal style. Now I'd like to know what above anouncement should be changed if we want to expressed in an informal style with ‘going to’.
1. At what time will the party begin\start?
Ans: The party will start at 10.00 pm.
2. When is the party going to start?
Ans: The party is going to start at 10.00 pm.
I would prefer using "is going" during a short notice (without a time frame, "mostly").
Note: you can use "going to" as well with the time frame. (but rare)
"will" is used to describe a future event with the time frame.
Formal\informal: I cannot vouch! Both sounds okay to me.