"Organizations count on systems administrators to ensure that their computers and software are fully functional. In an interview, expect technical questions that will test your ability to troubleshoot relevant computer issues. Because systems administrators often play the role of customer supporter, be prepared to answer a situational question about dealing with a difficult customer. In addition, make sure to highlight your interpersonal and communication strengths as well as your ability to clearly explain technical concepts to a non-technical audience."
if file permissions is set to 755, is that file can be accessed by anybody
yes, the file can be accessed be anyone.
Initial thought would lead you to believe that 755 simply means read/execute for group and others. BUT!... if the directory cannot not be searched by the user, then the file cannot be accessed by the user. Consider a file that is 755 in a folder that is 700. That file cannot be access by anyone but the owner and root even though it is 755. All higher level folders must be searchable (x bit) in order for the 755 file's inode to be read. A 755 file can be accessed if all parental folders have the execute bit set for the accessing user.