The number of natural numbers less than 1000 in which no two digits are repeated is

No. of one digit natural numbers=9 

No. of two digit      "             "        =9(9p1)  

No. of   3   digit      "             "        =9(9p2)  

Total no. of natural numbers less than 1000

$$\begin{gathered} =9+9\left(9\right)+9(9\times 8) \\ =9(1+9+72)=738 \end{gathered}$$