Given $30!$ ends with some zeros, what is the digit that immediately precedes these zeros?

Compute $3^{2017}\pmod{1000}$.

Let integer $N=\left\lfloor{(\sqrt{29}+\sqrt{21})^{2020}}\right\rfloor$ where $\lfloor{x}\rfloor$ denotes the largest integer not exceeding $x$. Find the last two digits of $N$.

Let the product of all odd positive integer not greater than $2019$ be $2019!!$. Find the last three digits of $2019!!$.

Find the last $4$ digits of $2018^{2019^{2020}}$.