list-stats.rb

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

def avg(array)
  sum = 0.0
  array.each do |x|
    sum += x
  end
  (sum / array.length).round(2)
end

def lowest(array)
  lowest = array[0]
  array.each do |x|
    if x < lowest
      lowest = x
    end
  end
  lowest
end

def highest(array)
  max = array[0]
  array.each do |x|
    if x > max
      max = x
    end
  end
  max
end

puts "Average score: #{avg(test_scores)}"
puts "Lowest score:  #{lowest(test_scores)}"
puts "Highest score: #{highest(test_scores)}"

Great work! This looks awesome.

If you wanted to shorten things up a tiny bit, you can use one-line syntax for do...end and if blocks:

def avg(array)
  sum = 0.0
  array.each { |x| sum += x }
  (sum / array.length).round(2)
end

def lowest(array)
  lowest = array[0]
  array.each { |x| lowest = x if x < lowest }
  lowest
end

I'd only use that syntax if you have just one line of code to run inside your block, although I think Sandi Metz uses curly braces for larger blocks.

Also, you can use inject to calculate the sum of an array of numbers.

Great job!