Python:

7. calculates the alternating sum of digits of Write a function that sum of digits of a number dod1d2 ..dn-idn in decimal representation is a number. The alternating do-d1 d2-d3 + ...- dn-1+dn assuming that n is even. For example, the alternating sum of digits of 123456 is 1-2 + 3-4 + 5-6 =-3. A Medium Access Control (MAC) address in human-friendly, canonical form is a string of six groups of two hexadecimal digits, separated by hyphens. A hexadecimal digit is one of 0 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f. An example for a valid MAC address in this format is 8. 12- f4 29- ae 34 - c3 Write a function that checks whether the string (provided as an argument) is a valid MAC address or not. 9. Given a list, return the list element that appears most frequently in the list