Get in touch
Whether you've found a typo, have a question about a chapter, or want to talk about advertising or a partnership, we'd like to hear from you.
Response time
Usually within 2–3 days
What to include
To help us answer quickly, it's useful to mention:
- Which chapter or page you're writing about, if relevant
- Whether you're reporting an error, asking a question, or something else
- Any screenshots or links, if you're reporting a display or quiz issue
Follow along elsewhere
You can also reach us, or just keep up with new lessons and quizzes, through our social channels:
Advertising & partnerships
This site carries advertising served through Google AdSense, which helps keep the course free for everyone. If you're interested in a partnership or have a question about advertising on the site, mention that in your email and we'll get back to you.