The number of 3 digit odd numbers, that can be formed by using the digits 1,2,3,4,5,6 when the repetition is allowed is

Extreme left place can be filled in 6 ways. The middle place can be filled in 6 ways and extreme right place in only 3 ways

               $(\because$  number to be formed is odd)

$\therefore$  Required number of numbers

             $=6\times 6\times 3=108$