Mentally calculating logarithms


#21

Using this knowledge, see if you can repeat these calculations:

Also, see if you can spot the 2.3… and .43… .


#22

What is best way to calculate mentally left to right or abacus?


#23

@Girish.
There is no “best” way to do anything, least of all mental calculation. In my opinion, mental math is at least a third of choosing the right method to do the calculation. It is extremely situational. So, it would be optimal to learn as many techniques as you could.

Back to the topic at hand, I think mentally calculation logarithms is a very interesting subject. Mainly for the reason that I’ve never seen anyone(until now!) capable of doing it mentally. I seem to be a few years late to the discussion, but perhaps a general method for approximating logarithms could be devised? I think the intent should be 4-digit decimal precision with minimum memorization.

And in case anyone is interested, the subject of ‘e’ is very fascinating. https://betterexplained.com/articles/an-intuitive-guide-to-exponential-functions-e/ has a very good explanation.


#24

I think this is what you are looking for: