diff --git a/Gemfile b/Gemfile
index fa75df1..a1b93f3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,3 @@
-source 'https://rubygems.org'
+source :rubygems
 
 gemspec
diff --git a/lib/core_ext/big_decimal.rb b/lib/core_ext/big_decimal.rb
index 2f88fc6..e07baef 100644
--- a/lib/core_ext/big_decimal.rb
+++ b/lib/core_ext/big_decimal.rb
@@ -1,9 +1,36 @@
-require 'corrency/corrency_mixin'
+require 'bigdecimal'
+require 'bigdecimal/util'
 
 class BigDecimal
-  include CorrencyMixin
 
-  def to_s(s = "%.2f")
-    sprintf(s, self)
+  def inc_vat
+    (self * vat_rate).to_d
   end
+  
+  def ex_vat
+    (self / vat_rate).to_d
+  end
+  
+  def next_ninety_nine
+    self.ceil - BigDecimal.new("0.01")
+  end
+    
+  def add_margin(margin)
+    ((self / (100 - margin)) * 100).to_d.round(2)
+  end
+
+  def margin(cost)
+    ((self - BigDecimal.new(cost)) / self) * 100
+  end
+  
+  old_to_s = instance_method :to_s
+
+  define_method :to_s do |*param|
+    "%.2f" % self.round(2)
+  end
+  
+  protected
+    def vat_rate
+      1 + (Corrency::Config.vat_rate.to_f / 100)
+    end
 end
diff --git a/lib/core_ext/fixnum.rb b/lib/core_ext/fixnum.rb
deleted file mode 100644
index c6cafd9..0000000
--- a/lib/core_ext/fixnum.rb
+++ /dev/null
@@ -1,5 +0,0 @@
-require 'corrency/corrency_mixin'
-
-class Fixnum
-  include CorrencyMixin
-end
diff --git a/lib/corrency.rb b/lib/corrency.rb
index 0f736b1..398e831 100644
--- a/lib/corrency.rb
+++ b/lib/corrency.rb
@@ -1,3 +1,2 @@
 require 'corrency/config'
-require 'core_ext/big_decimal'
-require 'core_ext/fixnum'
+require 'core_ext/big_decimal'
\ No newline at end of file
diff --git a/lib/corrency/corrency_mixin.rb b/lib/corrency/corrency_mixin.rb
deleted file mode 100644
index 7f4f73c..0000000
--- a/lib/corrency/corrency_mixin.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-require 'bigdecimal'
-require 'bigdecimal/util'
-
-module CorrencyMixin
-  def inc_vat
-    (self.to_d * vat_rate)
-  end
-
-  def ex_vat
-    (self.to_d / vat_rate)
-  end
-
-  def next_ninety_nine
-    self.ceil - BigDecimal.new("0.01")
-  end
-
-  def add_margin(margin)
-    ((self.to_d / (100 - margin.to_d)) * 100).round(2)
-  end
-
-  def margin(cost)
-    self_d = self.to_d
-    ((self_d - BigDecimal.new(cost)) / self_d) * 100
-  end
-
-  protected
-    def vat_rate
-      1 + (Corrency::Config.vat_rate.to_d / 100)
-    end
-end
diff --git a/test/big_decimal_test.rb b/test/big_decimal_test.rb
index d876219..f153321 100644
--- a/test/big_decimal_test.rb
+++ b/test/big_decimal_test.rb
@@ -8,17 +8,13 @@
       @bd = BigDecimal.new('100.3799')
       assert_equal("100.38", BigDecimal.new("100.38000123").to_s)
     end
-
+    
     it "should round to two decimal places if 0" do
       assert_equal "0.00", BigDecimal.new("0").to_s
     end
-
+    
     it "should round to two decimal places if 1.20" do
       assert_equal "1.20", BigDecimal.new("1.2").to_s
     end
-
-    it "should accept a format override" do
-      assert_equal '31.4159', BigDecimal.new('31.4159265358979').to_s('%.4f')
-    end
   end
 end
diff --git a/test/fixnum_test.rb b/test/fixnum_test.rb
deleted file mode 100644
index 044bcf6..0000000
--- a/test/fixnum_test.rb
+++ /dev/null
@@ -1,13 +0,0 @@
-require 'test_helper'
-
-describe Fixnum do
-
-  describe "#inc_vate" do
-
-    it "should return the same as a BigDecimal does" do
-      [0, 3, 1000].each do |num|
-        assert_equal(num.inc_vat, BigDecimal.new(num).inc_vat)
-      end
-    end
-  end
-end