A shop sells pencils only in boxes of fixed size.  

It cannot sell 100 pencils.  

It can sell any larger amount of pencils.

It has one of each size box on display.

question 1: What is the minimum amount of boxes it may have on display?  

question 2: What is the minimum amount of pencils it may have on display?

example: If the shop would sell boxes with 5,8, 28 and 100 pencils, it would have 4 boxes / 141 pencils on display. In that case it would be able to sell any amount >100, but it could also sell 100 so it is not a valid solution.