The best educated Americans live mainly in the northeastern United States or in California, a new study finds. Zippia.com, a career resource website, studied education levels in all 50 states. It found that 40 percent of adults in Massachusetts have at least a bachelor’s degree. They completed a four-year study program at a college or university. Just three percent of Massachusetts high school students withdrew from school before finishing their studies. Other states on the top 10 list are Vermont, Virginia, New Hampshire, Connecticut, New Jersey, Minnesota, Maryland and Nebraska. California finished in 10th place on the rankings. Mississippi was ranked at the bottom of the list. Just 20 percent of adults there went to college. Other states near the bottom were Louisiana, Nevada, Oklahoma and Arkansas.