Andrea Vike, age 10, of Springfield, Ore., for her question:

HOW DOES THE ZIP CODE WORK?

After much deliberation and study, the people in the U.S. Postal Service  then called the Post Office Department   knew they had to come up with a system of coding all mail that would help to speed it on its way toward faster delivery. By 1963, when the ZIP Code system went into operation, the volume of mail in the United States had increased 900 percent since 1900.

ZIP sounds as if the word was taken from "zipping along.'' Although that's certainly the idea of the system, the word actually stands for Zoning Improvement Plan.

ZIP Coding directs that you put five numerals after an address when you are sending a letter. In Springfield, Ore., for example, the ZIP Code is 97477.

The first number in a ZIP Code designates one of 10 geographical areas of the country. The number 9 is used for the three West Coast states and Alaska and Hawaii. Number 2, for example, covers the District of Columbia, Maryland, North Carolina, South Carolina, Virginia and West Virginia.

The second and third numbers in a ZIP Code indicate a metropolitan area or sectional center, while the final two numbers pinpoint the area to a small town or individual delivery unit from which the mail is delivered.

Also in 1963, at the same time it introduced the AIP Code system, the Post Office Department came up with an approved two letter abbreviation for each of the states. The idea was to enable mechanized addressing systems to save space by putting a ZIP Code on the same line of an address as the city and state.

The Post Office state abbreviations, in most cases, are the first two letters of the state's name. AL is Alabama and AR is Arkansas. There are some exceptions, however:

AK is Alaska, AZ is Arizona, CT is Connecticut, GA is Georgia, HI is Hawaii, IA is Iowa, KS is Kansas, KY is Kentucky, LA is Louisiana, ME is Maine, MD is Maryland, MN is Minnesota, MS is Mississippi, MO is Missouri, MT is Montana, NV is Nevada, PA is Pennsylvania, TN is Tennessee, VT is Vermont and VA is Virginia.

All states having two words, such as New York and North Carolina, take the first initial of each of the two words   for example NY and NC.

Postal authorities report that the trend of mail changed a great deal between 1900 and the present time. In the earlier period, most mail was personal while now more than 80 percent of it is business correspondence. ZIP Codes, the people at the Post Office report, are especially helpful in speeding up the handling of business bulk mail.