One number is selected at random from the four digit numbers that can be formed from the digits 1, 2, 3, 4, 5, 6, 7. Then the probability that it is an odd number is

$$\begin{gathered} {\text{The number of four digit numbers that can be formed from the digits 1,2,3,4,5,6,7 is 7}}^4 \\ {\text{n(S)=7}}^4 \end{gathered}$$  

Suppose that E be the event of getting odd number. 

To get the number of odd numbers, place any of the odd number in the unit place, this can be done in 4 ways

the remaining three blanks with seven digits can be filled in  $7^4$ ways. 

$n\left(E\right)=7^3\times 4$

$Therefore, the required probability is P\left(E\right)=\frac{7^3\times 4}{7^4}=\frac{4}{7}$