diff --git a/pattern_generator/lib/generator.rb b/pattern_generator/lib/generator.rb
new file mode 100644
index 0000000..9f3af67
--- /dev/null
+++ b/pattern_generator/lib/generator.rb
@@ -0,0 +1,41 @@
+class Generator
+  attr_accessor :pattern_count
+
+  LETTERS = Array('A'..'Z')
+  NUMBERS = Array(0..9)
+
+  def initialize
+    @pattern_count = 1
+    @serial_number = ''
+  end
+
+  def random_letters(pattern)
+
+    pattern.each_char do |char|
+      if char == "X"
+        letter = LETTERS.sample
+        pattern_counter(26)
+        @serial_number << letter
+      elsif char == "N"
+        number = NUMBERS.sample
+        pattern_counter(10)
+        @serial_number << number
+      end
+    end
+    @serial_number
+  end
+
+  def pattern_counter(multiplier)
+    @pattern_count = @pattern_count*multiplier
+  end
+
+  def all_combinations(pattern)
+    LETTERS.repeated_permutation(pattern.length).to_a
+  end
+
+  def combination_count(pattern)
+    random_letters(pattern)
+    @pattern_count
+  end
+
+end
diff --git a/pattern_generator/readme b/pattern_generator/readme
new file mode 100644
index 0000000..bc73d6e
--- /dev/null
+++ b/pattern_generator/readme
@@ -0,0 +1,14 @@
+# Pattern Generator
+
+We want to generate serial numbers for our products as they roll off the manufacturing line. Patterns for the
+numbers are five characters like `XXNXN` where `X` stands for an uppercase letter A-Z and `N` stands for a digit 0-9.
+
+Write a program which, given a pattern like `XXNXN`, can both:
+
+* generate all possible serial numbers for that pattern
+* report out how many numbers were generated.
+
+## Extensions
+
+* Can you also support patterns of any length?
+* Customers often confuse `0` and `O`, `I` and `1`. Let's omit all four of those symbols from the generator.
diff --git a/pattern_generator/test/generator_test.rb b/pattern_generator/test/generator_test.rb
new file mode 100644
index 0000000..771da97
--- /dev/null
+++ b/pattern_generator/test/generator_test.rb
@@ -0,0 +1,118 @@
+gem 'minitest', '>= 5.0.0'
+require 'minitest/pride'
+require 'minitest/autorun'
+require './lib/generator'
+require 'pry'
+
+class GeneratorTest < Minitest::Test
+
+  def test_it_exists
+    
+    g = Generator.new
+    assert g
+  end
+
+  def test_it_generates_a_single_letter
+    
+    g = Generator.new
+    code = g.random_letters("X")
+
+    assert_equal 1, code.length
+    assert_equal String, code.class
+  end
+
+  def test_it_generates_five_letters
+    
+    g = Generator.new
+    code = g.random_letters("XXXXX")
+
+    assert_equal 5, code.length
+    assert_equal String, code.class
+  end
+
+  def test_it_generates_a_letter_and_number
+    
+    g = Generator.new
+    code = g.random_letters("XN")
+
+    assert_equal 2, code.length
+    assert_equal String, code.class
+  end
+
+  def test_it_generates_a_letter_number_combo
+    
+    g = Generator.new
+    code = g.random_letters("XNXXN")
+
+    assert_equal 5, code.length
+    assert_equal String, code.class
+  end
+
+  def test_it_generates_all_combos_for_1_letter
+    
+    g = Generator.new
+    pattern = "X"
+    combos = g.all_combinations(pattern)
+
+    assert_equal 26, combos.count
+    assert_equal Array, combos.class
+  end
+
+  def test_it_generates_all_combos_for_2_letters
+
+    g = Generator.new
+    pattern = "XX"
+    combos = g.all_combinations(pattern)
+
+    assert_equal 676, combos.count
+    assert_equal Array, combos.class
+  end
+
+  def test_it_generates_all_combos_for_1_letter_1_number
+
+    g = Generator.new
+    pattern = "XN"
+    combos = g.all_combinations(pattern)
+
+    assert_equal 260, combos.count
+    assert_equal Array, combos.class
+  end
+
+  def test_it_counts_all_combos_for_2_letters
+
+    g = Generator.new
+    pattern = "XX"
+    combos = g.combination_count(pattern)
+
+    assert_equal 676, combos
+  end
+
+  def test_it_counts_all_combos_for_1_letter_1_number
+    
+    g = Generator.new
+    pattern = "XN"
+    combos = g.combination_count(pattern)
+
+    assert_equal 260, combos
+  end
+
+  def test_it_generates_all_combos_for_5_letters
+    
+    g = Generator.new
+    pattern = "XXXXX"
+    combos = g.all_combinations(pattern)
+
+    assert_equal 11881376, combos.count
+    assert_equal Array, combos.class
+  end
+
+  def test_it_count_total_combos_for_5_letters
+    
+    g = Generator.new
+    pattern = "XXXXX"
+    combos = g.combination_count(pattern)
+
+    assert_equal 11881376, combos
+  end
+
+end