Asked by Suhas v | 17th Jan, 2014, 03:44: PM

Expert Answer:

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

Answered by Vimala Ramamurthy | 17th Jan, 2014, 09:40: PM

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