Group Activity Cards

 Statistics and Probability Use groups of 2. A Not-So-Secret Code

ZIP (zone improvement plan) codes have been around since 1963. Letters with ZIP codes can be sorted and delivered by the United States Postal Service much more quickly than letters without ZIP codes.

The standard ZIP code is a five-digit number. The first digit identifies a region of the United States. The next two digits, together with the first digit, identify a section (often a large city). The last two digits identify key post offices within the section. Sometimes you see nine-digit ZIP codes (ZIP + 4). The four additional digits identify individual postal routes at the key post offices.

Answer the questions shown below. Assume that there are no restrictions on the use of digits.

 1 What is the greatest number of sections within each region? 2 What is the greatest number of key post offices within each section? 3 What is the greatest number of individual postal routes for a key post office? 4 How many different five-digit ZIP codes are possible in the United States? 5 Tell why you think the basic ZIP code has five digits instead of four or six.

Indiana