Consider the number from $\mathrm{000,} \mathrm{001,} 002,....., \mathrm{998,} 999.$
Since, each digit has an equal likelihood of coming and digits used are $3\times 1000.$
Hence, 0 appears $=300$ times
But, $\mathrm{000,001,002},....,\mathrm{098,099};$
have some unwanted zeros, we subtract
these zero’s i.e. $3\times 1+2\times 9+1\times 90=111.$
Thus, total times 0 appears $=300-111=189$
Also, add $3$ zero’s in 1000.
$\Rightarrow 189+3=192.$