A teacher has 10 books on a shelf. There are 6 mechanics books A, B, C, D, E, and F. There are 4 statistics books W, X, Y and Z.The books are now placed on the shelf with the mechanics books together at the left end and the statistics books together at the right end. Within each section the books can be arranged at random. Find the probability that book A and book Z have at least 7 books between them.
