def as_hours hours
      minutes = hours.to_f * 60.0
      sprintf "%d:%02d", (minutes / 60).to_i, (minutes % 60).to_i
    end
def as_hours hours
      minutes = hours.to_f * 60.0
      sprintf "%d:%02d", (minutes / 60).to_i, (minutes % 60).to_i
    end
Convert from decimal to a string of the form HH:MM.

 @param [#to_f] hours number of hours in decimal
 @return [String] of the form "HH:MM"