1.

LAst digit can be filled in 4 ways (1,3,5,7)

 

Second digit can be filled in 6 ways as one of 7 digits has been used and repetition is not allowed.

 

Similarly, first digit can be filled in 5 ways.

 

Thus number of ways of forming a three digit odd number without repetition is :

5 x 6 x 4 =120

 

2.

LAst digit can be filled in 4 ways (1,3,5,7)

 

Second digit can be filled in 7 ways as repetition is allowed.

 

Similarly, first digit can be filled in 7 ways.

 

Thus number of ways of forming a three digit odd number with repetition is :

7 x 7 x 4 =196