Hey!
Finding the factorial for the first few numbers, we have:
1!=1
2!=2
3!=6
4!=24
5!=120
6!=720
7!=720*7
8!=720*56
What we can see as a clear pattern from 5! and on is that our number ends with a 0, making the units digit 0. Therefore, when we add the units digit of 5! and on, we have a result of 0. So, we can simply add the units digits of 1!, 2!, 3!, and 4!, which is 1+2+6+4=13. Since the units digit is the last number, we can drop the tens place to get an answer of 3.
Feel free to ask further questions!
The square root of 75 is 8.66, so it would be between 8 and 9
