To answer your question, I will first explain the differences between 'fewer' and 'less'. You would use 'fewer' when talking about people or when talking about objects/things in the plural. So, for example; "she has fewer shoes than I do" or "fewer students are choosing to study science". You cannot say "few fewer", just "fewer". You would use the word 'less' when talking about something that cannot be counted, or something that doesn't have a plural (money, air, time, music, rain). So you could say "I have less money than she does" or "people want to spend less time in traffic jams". You can also use the word 'less' when talking about numbers in terms of measurements. An example would be "the McDonalds is less than 1 mile away" or "I used to weigh 112kg, but now I weigh less than 100kg".