1. Letters adjoined: h, i, o.

State added: Ohio.

2. Letters adjoined: a, w.

States added: Iowa, Hawaii.

3. Letters adjoined: d, n.

States added: Idaho, Indiana.

4. Letters adjoined: k, l, s.

States added: Alaska, Illinois, Kansas.

5. Letters adjoined: b, e, r.

States added: Arkansas, Delaware, Nebraska, Rhode Island.

6. Letter adjoined: m.

States added: Alabama, Maine, Oklahoma.

7. Letter adjoined: t.

States added: Minnesota, Montana, North Dakota, Tennessee.

8. Letters adjoined: c, g.

States added: Colorado, Georgia, Michigan, North Carolina, Oregon, Washington, Wisconsin.

9. Letter adjoined: u.

States added: Connecticut, Louisiana, Massachusetts, Missouri, South Carolina, South Dakota, Utah.

10. Letter adjoined: y.

States added: Kentucky, Maryland, New York, Wyoming.

11. Letter adjoined: v.

States added: Nevada, Vermont, Virginia, West Virginia.

12. Unused letters: f, j, p, x, z.

States not yet spelled: Arizona, California, Florida, Mississippi, New Hampshire, New Jersey, New Mexico, Pennsylvania, Texas.

Extra credit:

The letter j appears only in New Jersey, and z only appears in Arizona. F can be found in California and Florida, and x in New Mexico and Texas. The letter p appears in Mississippi, New Hampshire, and Pennsylvania. Because the letter b occurs in only two states (Alabama and Nebraska), if we had omitted b from our list of 20 letters and adjoined p instead, we would have a total of 42 states using only 20 different letters.