Number theory Week 2 Challenge question 10

Week 2 Challenge question 10
Suppose that the prime factors of an odd number only occur once in its prime factorization, so that n=p1xp2xp3xp4x...
for prime integers p1,p2,p3,...
What must be true about the average of all the positive integer factors of n?
Correct answer is : The average of the positive integer factors of n will be a whole number.Couldn't understand the explanation provided. Could you explain for explicit?
For example n=5x7x11, the average sum should be (5+7+11)/3 isn't an integer? 
@versatilewhale Thank you for writing! Since this is an exam question, I'll answer over email if that's okay. We don't want to "spill the beans."

@debbie Please do.

@versatilewhale Hi there, I just wrote to you over email. I just realized that I can privatemessage you on the forum as well. So I'll go and do that right now!

@debbie I just privatemessaged you my reply! You can click on the speechbubble icon in the top right next to your profile pic to view your messages.

@debbie Thx for explanation. I didn't get the question earlier, forgot it mentioned in Day 5.