What percentage of the stuff on the internet is true?

Absolutely not!

Anything that is a "wiki", for example, may be added to by anyone, and some people find it amusing to type in totally ridiculous answers. People can put what they want to put on their own websites and blogs. You need to be able to separate fact from fiction.

If you're looking for medical information, a site affiliated with a hospital or research center (or the NIH- National Institute of Health) is a better choice than a site written by someone random.

For school information, you probably want to go to more than one place. A celebrity biography site maintained (or endorsed) by the celebrity or the family is better than a fan site for accuracy of information.

If the website is trying to sell you something, check the record they have with the Better Business Bureau. If it's a charity, you should be able to check to see if it's registered with the government.

To check out a strange story, try googling "Snopes" or "Urban Legends."

Don't believe everything you see, read, or hear.