Rails can't find installed gem

I'm following a tutorial for Rails that specifically asks for version 4.2.0 so I installed Rails with sudo gem install rails -v 4.2.0 and it worked fine. When I try to create a new application with rails _4.2.0 new test_app I get an error message that says /Library/Ruby/Site/2.0.0/rubygems/dependency.rb.315: in 'to_specs': Could not find 'railties' (=4.2.0) - did find: [railties-4.2.1] (Gem::LoadError) and continues on for a little bit more.

I've tried installing that specific version of railties with sudo gem install railties -v 4.2.0 but I still get the same error. Is it checking for/installing the gem in two different places?

EDIT: Running gem list yields the following output, clearly showing railties (4.2.0):

*** LOCAL GEMS ***

actionmailer (4.2.0)
actionpack (4.2.1, 4.2.0)
actionview (4.2.1, 4.2.0)
activejob (4.2.1, 4.2.0)
activemodel (4.2.0)
activerecord (4.2.0)
activesupport (4.2.1, 4.2.0)
arel (6.0.0)
bigdecimal (1.2.6)
builder (3.2.2)
bundler (1.9.9)
erubis (2.7.0)
globalid (0.3.5)
i18n (0.7.0)
io-console (0.4.3)
json (1.8.2, 1.8.1)
loofah (2.0.2)
mail (2.6.3)
mime-types (2.6.1)
mini_portile (0.6.2)
minitest (5.6.1, 5.4.3)
nokogiri (1.6.6.2)
power_assert (0.2.2)
psych (2.0.8)
rack (1.6.1)
rack-test (0.6.3)
rails (4.2.0)
rails-deprecated_sanitizer (1.0.3)
rails-dom-testing (1.0.6)
rails-html-sanitizer (1.0.2)
railties (4.2.0)
rake (10.4.2)
rdoc (4.2.0)
sprockets (3.1.0)
sprockets-rails (2.3.1)
test-unit (3.0.8)
thor (0.19.1)
thread_safe (0.3.5)
tzinfo (1.2.2)