Multiple entry, are all incoming and outgoing flights or train tickets necessary to apply?

Next month I fly to Beijing and after one week here I will go to Mongolia for 3 weeks and come back to China for 4 more weeks before I go to Hongkong and fly to the philipines from there. I have booked the ticket to Beijing and the ticket from hong kong to the philipines. Do I need to book the train to Mongolia as well in order to apply for a visa?