Any person interested may contest the petition by filing written opposition thereto, on the ground of the incompetency of the applicant, or may, at any time within thirty (30) days after an administrator has been appointed, assert his own rights to the administration and pray that letters be issued to himself. In the latter case the contestant must file his petition in the court. The court thereof shall set a day for hearing the same and the contestant shall give written notice by mail, postage prepaid, to the known heirs and the original petitioner or administrator, if the appointment has been made, of said contest, and the time and place set for hearing the same, at least five (5) days before said hearing.