First five problems in Ruby and (mostly) simplified to one-liners.

Ruby/1-a.rb

@@ -0,0 +1,10 @@
+#!/usr/bin/env ruby
+
+sum = 0;
+(1..999).each do |i|
+	if(i % 3 == 0 || i % 5 == 0) then
+		sum += i
+	end
+end
+
+puts sum

Ruby/1-b.rb

@@ -0,0 +1,6 @@
+#!/usr/bin/env ruby
+
+sum = 0;
+(1..999).each { |i| sum += i if (i % 3 == 0 || i % 5 == 0) }
+
+puts sum

Ruby/1-c.rb

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+
+puts (1...1000).select{ |i| i % 3 == 0 || i % 5 == 0 }.inject(:+)

Ruby/2-a.rb

@@ -0,0 +1,11 @@
+#!/usr/bin/env ruby
+
+sum = 0
+i = j = 1
+
+until (i >= 4000000)
+	i, j = j, i + j
+	sum += i if(i.even?)
+end
+
+puts sum

Ruby/2-conrad.rb

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+
+puts Enumerator.new { |yielder| i, j = 0, 1; loop {i, j = j, i + j; yielder.yield i} }.take_while { |n| n <= 4E6}.select { |i| i.even? }.inject(:+)

Ruby/3-a.rb

@@ -0,0 +1,4 @@
+#!/usr/bin/env ruby
+
+require 'prime'
+puts Prime.prime_division(600851475143).last[0]

Ruby/4-a.rb

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+
+p (100...1000).to_a.map{ |i| (100...1000).to_a.map{ |j| i *j } }.flatten(1).select { |i| i.to_s == i.to_s.reverse }.sort.last

Ruby/5-a.rb

@@ -0,0 +1,20 @@
+#!/usr/bin/env ruby
+
+i = 20
+while true do 
+	20.downto(1) { |j|
+		break if i % j != 0
+		@done = true if j == 1
+	}
+
+	break if @done
+
+	if i > 232792560 then
+		puts 'fail'
+		break
+	end
+
+	i += 20
+end
+
+puts i

Ruby/5-b.rb

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+
+ puts (1..20).inject(1) { |lcm, n| lcm.lcm(n) }