Resubmitted to show I now understand the concept.

checkin2.rb

numbers= [75, 100, 85, 65, 84, 87, 95]

def average (numbers)
  sum=0
  numbers.each do |num|
  sum += num
  end

  sum/numbers.length.to_f
end


def lowest (numbers)
     minimum=numbers[0]
     numbers.each do |num|
      if num<minimum
        minimum=num
      end
    end
      minimum
    end


def highest(numbers)
  maximum=numbers[0]
  numbers.each do |num|
    if num > maximum
      maximum = num
    end
  end
  maximum
end

puts average(numbers)
puts lowest(numbers)
puts highest(numbers)