Why are you splitting the string more than once..save it as a variable
Why are you mapping over the split string...and then iterating again to see if all the elements in the map are true? Why not just use s.split.all?{|w| numbers.include?(w)}

Again, you mapping over string...and then iterating again using reduce...just pass a block into reduce:
avg = s.split.reduce(0){|acc,el| acc + numbers.index(el)} / s.split.count

use a new line

use a new line

always good to know when to use a new line

odd use of case statment.