Question 17
If $n$ is an even positive integer, the double factorial notation $n!!$ represents the product of all the even integers from $2$ to $n.$ For example:
$$
8!! = 2 \times 4 \times 6 \times 8
$$
What is the units digit of the following sum?
$$
\begin{aligned} &2!! + 4!! + 6!! + \cdots \\ &\quad {}+ 2018!! + 2020!! + 2022!! \end{aligned}
$$
$$
8!! = 2 \times 4 \times 6 \times 8
$$
What is the units digit of the following sum?
$$
\begin{aligned} &2!! + 4!! + 6!! + \cdots \\ &\quad {}+ 2018!! + 2020!! + 2022!! \end{aligned}
$$