GMAT Verbal Section | Re: Fewer Vs Less

I understand if I can count something I use "fewer" and use "less" for something I cannot count (ie, gas, water and etc)
However, ON GMAT, (I honestly don't care what others have to say) if it's percentage, or unit of measure (miles, grams, squarefeet and ect), Do I need to use "fewer" or "less"?

I ran 4 miles fewer than Andy.

We can certainly count how many more miles I ran than Andy did...

I consumed 30% fewer calories