diff --git a/lib/liquid/standardfilters.rb b/lib/liquid/standardfilters.rb
index 19ace466..6128f785 100644
--- a/lib/liquid/standardfilters.rb
+++ b/lib/liquid/standardfilters.rb
@@ -185,22 +185,35 @@ module Liquid
     
     # addition
     def plus(input, operand)
-      input + operand if input.respond_to?('+')
+      to_number(input) + to_number(operand)
     end
     
     # subtraction
     def minus(input, operand)
-      input - operand if input.respond_to?('-')
+      to_number(input) - to_number(operand)
     end
     
     # multiplication
     def times(input, operand)
-      input * operand if input.respond_to?('*')
+      to_number(input) * to_number(operand)
     end
     
     # division
     def divided_by(input, operand)
-      input / operand if input.respond_to?('/')
+      to_number(input) / to_number(operand)
+    end
+    
+    private
+    
+    def to_number(obj)
+      case obj
+      when Numeric
+        obj
+      when String
+        (obj.strip =~ /^\d+\.\d+$/) ? obj.to_f : obj.to_i
+      else
+        0
+      end
     end
     
   end
diff --git a/test/standard_filter_test.rb b/test/standard_filter_test.rb
index 916c1139..9c442e1c 100644
--- a/test/standard_filter_test.rb
+++ b/test/standard_filter_test.rb
@@ -131,18 +131,29 @@ class StandardFiltersTest < Test::Unit::TestCase
   
   def test_plus
     assert_template_result "2", "{{ 1 | plus:1 }}"
-    assert_template_result "11", "{{ '1' | plus:'1' }}"
+    assert_template_result "2.0", "{{ '1' | plus:'1.0' }}"
   end
   
   def test_minus
     assert_template_result "4", "{{ input | minus:operand }}", 'input' => 5, 'operand' => 1
+    assert_template_result "2.3", "{{ '4.3' | minus:'2' }}"
   end
   
   def test_times
     assert_template_result "12", "{{ 3 | times:4 }}"
-    assert_template_result "foofoofoofoo", "{{ 'foo' | times:4 }}"
+    assert_template_result "0", "{{ 'foo' | times:4 }}"
+    assert_template_result "6.3", "{{ '2.1' | times:3 }}"
+    assert_template_result "6", "{{ '2.1' | times:3 | replace: '.','-' | plus:0}}"
   end    
   
+  def test_divided_by
+    assert_template_result "4", "{{ 12 | divided_by:3 }}"
+    assert_template_result "4", "{{ 14 | divided_by:3 }}"
+    assert_template_result "4.66666666666667", "{{ 14 | divided_by:'3.0' }}"
+    assert_template_result "5", "{{ 15 | divided_by:3 }}"
+    assert_template_result "Liquid error: divided by 0", "{{ 5 | divided_by:0 }}"
+  end
+  
   def test_append
     assigns = {'a' => 'bc', 'b' => 'd' }
     assert_template_result('bcd',"{{ a | append: 'd'}}",assigns)        
@@ -155,10 +166,8 @@ class StandardFiltersTest < Test::Unit::TestCase
     assert_template_result('abc',"{{ a | prepend: b}}",assigns)        
   end
   
-  def test_divided_by
-    assert_template_result "4", "{{ 12 | divided_by:3 }}"
-    assert_template_result "4", "{{ 14 | divided_by:3 }}"
-    assert_template_result "5", "{{ 15 | divided_by:3 }}"
+  def test_cannot_access_private_methods
+    assert_template_result('a',"{{ 'a' | to_number }}")
   end
   
 end