Question

How do I find the approximate value of `log_5 100`?

Answer 1

Well, for starters, remember that logs are really just powers in reverse!
If you know some powers of 5, then just keep going...
`5^2=25` and `5^3=125` , so the answer must be between 2 and 3.
Use a scientific calculator (at least) to continue guessing:

However, some calculators will give you a much better answer, and much faster:

If you don't have this kind of option on your calculator, try some online: Online log calc