diff --git a/.travis.yml b/.travis.yml
index d26fd4b..a9445a8 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,7 @@ cache: bundler
 bundler_args: --retry=3 --jobs=3
 language: ruby
 rvm:
+  - 2.4.1
   - 2.3.0
   - 2.1.8
   - 2.2.4
diff --git a/code/enumerable/inject-symbol-plus-vs-sum.rb b/code/enumerable/inject-symbol-plus-vs-sum.rb
new file mode 100644
index 0000000..780f093
--- /dev/null
+++ b/code/enumerable/inject-symbol-plus-vs-sum.rb
@@ -0,0 +1,19 @@
+require "rubygems"
+require "benchmark/ips"
+
+ARRAY = (1..1000).to_a
+
+def fast
+  ARRAY.sum
+end
+
+def slow
+  ARRAY.inject(:+)
+end
+
+Benchmark.ips do |x|
+  x.report('sum')                { fast }
+  x.report('inject symbol plus') { slow }
+
+  x.compare!
+end