Find the number of ways of arranging the numbers 1,2 ,3, 4, 5, 6, 7, 8, 9 in a row so that the product of any two adjacent numbers is even.
1, 3, 5, 7, 9 ==5!
2, 4, 6, 8 ==4!
Total number of arrangements==5! x 4! ==120 x 24 ==2,880 such permutations.
