The number of odd numbers having 4 digits can be formed from {1, 2, 3, ......., 9} are

{1,2,3,....9} is the given set of digits. consider 4 places. For odd numbers units place can filled using 1,3,5,7,9 in

 5 ways. Remaining 3 places can be filled using remaining 8 digits in${ }^8{P}_3$  ways.

∴ No. of permutations=5$\left({ }^8{P}_3\right)$=5(8×6×7)                                                        

                                       = 1680