Number Theory: Last digits

$9! = 36288\fbox 0$

Or:

$2 \times 5 = 10 = \fbox 0$

The most easiest part is that when it's multiply by 5 in any even number, the last digit will be 0. As we all know:

2 x 5 = 1 [0] 4 x 5 = 2[0] etc.

Solution 1: Observe that since we have $2 \times 5$ , the product is a multiple of $10.$ No matter what other factors there are, having a multiple of $10$ indicates the last digit will be a $0.$

Solution 2: We can perform the tedious calculation, to find that the product is $\num{362880}.$ Thus, the last digit is $0.$