CAT 2023 Slot 1 Solved Paper

1-digit numbers $\Rightarrow$ We have 1 to $9\Rightarrow 9$
2-digit numbers $\Rightarrow \mathit{x}\mathit{y}$, we have 9 ways to choose $\mathit{x}$ from 1 to $9\Rightarrow 9$ ways and 9 ways to choose $\mathit{y}$ ( 0 to 9 except $\mathit{x})\Rightarrow 9*9=81$
3-digit numbers $\Rightarrow \mathit{x}\mathit{y}\mathit{z}$, we have 9 ways to choose $\mathit{x},9$ ways to choose $\mathit{y}$ and 8 ways to choose $\mathit{z}\Rightarrow 9*9*8=$ 648.
Total numbers till 1000 without digits repeated in them is $9+81+648=738$.