Primary U.S. interstate highways are numbered 1-99. Odd numbers (like the 5 or 95) go north/south, and events (like the 10 or 90
) go east/west. Auxiliary highways are numbered 100-999, and service the primary highway indicated by the rightmost two digits. Thus, the 405 services the 5, and the 290 services the 90. Given a highway number, indicate whether it is a primary or auxiliary highway. If auxiliary, indicate what primary highway it serves. Also indicate if the (primary) highway runs north/south or east/west.
For instance, I-24 is a primary highway that runs east/west.
Explanation:
Based on information provided by the question, all numbers equal or below 99 are primary highways. If an even number, then it should run from east to west. If the primary highway is an odd number, it means that it runs from north to south. If the number is between 100 - 999, it is an auxiliary highway and the last two digits correspond to the primary highway that it serves.
Interstate Number 205 in Portland, OR on the west coast of the US is an auxiliary highway that runs North and South. I-205 serves the primary interstate 5 that also runs North and South through all of Washington, Oregon, and California.
