summing_multipules.rb

first = 0
last  = 1000
total = 0
multipules = []

# build the array of multipules
(first..last).each do |list|
  if (list % 5 == 0) or (list % 3 == 0)
     multipules.push(list)
  end
end

# add them up
multipules.each do |multipule|
  total += multipule
end

puts "Total is: #{total}"

# ========================================

# Or make your own `sum` method on array

class Array
  def sum
    total = 0
    self.each { |number| total += number }
    total
  end
end

puts "Total is: #{multipules.sum}"