ITOT 44 Spring 2023 · THPT · O (Basic) Question 2

For a nonnegative integer $n$, define $Q(x)=\lfloor x\rfloor+\lfloor x/2\rfloor+\cdots+\lfloor x/10^n\rfloor$. Find $Q(10^n)-Q(10^n-1)$. Here $\lfloor x\rfloor$ is the greatest integer not exceeding $x$.