Calculating logarithms in your head

[lockeisback]

am i the first to notice that 60 doesnt equal 2^3x3x5? that would be 120, i think he meant 2^2x3x5

[rickypen]

Thanks brother. No calculator on Mcat...this is huge

[LaneyAlora]

A skill I’ve been lacking for many years learned in five minutes. So helpful! Thank you!!

[okboing]

i don't know if you mentioned this in your video but i was recently trying to figure how to use log base n in .js but there weren't any commands i could find. i was astounded to find i could instead of writing log base x of y, i could write log(y) / log(x) where x is the base and y is the input

[Ensign_Cthulhu]

Came back to this via a circuitous route (noted my own comment below) and thought to myself, "How big a log table can I actually build using these five quantities and no others?" I recently stumbled on the fact that it is possible to approximate log 1.1 using the logs of 2, 3 and 7 only. To wit, one can construct log 108 from logs 2 and 3, and log 112 from logs 2 and 7, and average them to estimate the log of 110... from which you may then subtract two to get the log of 1.1.

Still working on some of the other two-digit primes. I was mildly concerned that using log 1.01 introduces artificial precision, as it extends to four DP whereas the others are truncated at three, but in fact a spreadsheet I'm building using these approximated values is not too far off percentage-wise from the actual logs as calculated (to eight SF) by Excel. You might not use it for engineering work, but it's a fun look at the way such tables can be built up from only a small number of starting values.

[CocoGras]

Thank you for all of your helpful math tips.

[quantumwaves]

Looked it up when I was super baked.... Currently trying to calculate laws of physics in the 4th dimension rn lol.

[TheREBwater]

Was looking for a way to calculate logarithms in my head (or on paper).

While this video is sort of neat, it is useful only if I memorize some rough approximations of other logarithms first...and those other logarithms were somehow calculated elsewhere. Could a presentation be made to show how to manually, by hand, calculate or derive the logarithm of any number directly?

I have a 19th-century book of seven-place logarithms. I'm sure this work was done without a calculator and I'd love to know HOW to work these out by hand. Just curious. Thanks.

[Ensign_Cthulhu]

This is excellent. Would you have any problem if I were to download this for offline viewing for my own use? I would not pass it on without attribution.

[yashu]

Thank you for making such an awesome video.

[omkakatkar]

is the same method applicable for prime numbers

[roonzacar]

Good video, how would you convert a number like 1.005 into a logarithm?

[ruleofrahul]

hi I am facing problem while calculating n in the following equation : 1.6^n=2 (1.6 raised to the power n is equal to 2) I tried your method. 60% increase means 60*0.004=0.240 but log1.6=0.204 and above method is giving it as 0.240 .Please help.