Question

What factorial equals 720?

Answer 1

Let's first do it the hard way.

Explanation:

You're trying to find out the solution for
`n! =720`
This means `1*2*3* ...*n=720`

You can divide by all consequtive numbers untill you end up with `1` as a result:
`720//1=720, 720//2=360,360//3=120` etc.

GC (TI-83):
MATH - PRB - !
And try a few numbers.

Answer: 6