Add Are They All True as a ruby til.

README.md

@@ -47,6 +47,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 
 ### ruby
 
+- [Are They All True?](ruby/are-they-all-true.md)
 - [Create an Array of Stringed Numbers](ruby/create-an-array-of-stringed-numbers.md)
 - [Limit Split](ruby/limit-split.md)
 - [Parallel Bundle Install](ruby/parallel-bundle-install.md)

ruby/are-they-all-true.md

@@ -0,0 +1,23 @@
+# Are They All True?
+
+There is a method on `Enumerable` that allows you to check against
+everything in a collection. This is the `all?` method.
+For instance, if you want to check if an array of values are all
+true, you can call it without arguments:
+
+```ruby
+> [true, true, true].all?
+# true
+> [true, false, true].all?
+# false
+```
+
+You can also pass it a block which is helpful if you want to check an
+attribute or method on a collection of objects, like so:
+
+```ruby
+> employees.all?(&:salaried?)
+# true
+> [1,2,3,4,5].all?(&:odd?)
+# false
+```