Credit card numbers follow certain patterns. a credit card number must have between 13 and 16 digits. the starting numbers are: 4 for visa cards, 5 for mastercard cards, 37 for american express cards, and 6 for discover cards. example: validating 4388576018402626 a) double every second digit from right to left. if doubling of a digit results in a two-digit number, add the two digits to get a single digit number.

Python. primary u.s. interstate highways are numbered 1-99. odd numbers (like the 5 or 95) go north/south, and evens (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.