Seeing numbers in Ruby with r attached to the number

0.1r      #=> (1/10)

0.1r * 3 #=> (3/10)

(0.5r..2r).step(0.1r).map &:to_f
#=> [0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0]