3 ms·
My approach: ln(19683) ~ ln(20000) = ln(20) + 3 ln(10) ~ 3 + 3*2.3 = 9.9. 3.3 = 1.0 + 2.3 ~ ln(e) + ln(10). My mental landmarks are ln(2), ln(e), and ln(10),
by cperciva 4y ago
My approach: ln(19683) ~ ln(20000) = ln(20) + 3 ln(10) ~ 3 + 3*2.3 = 9.9. 3.3 = 1.0 + 2.3 ~ ln(e) + ln(10).
My mental landmarks are ln(2), ln(e), and ln(10), roughly 0.7, 1.0, and 2.3 respectively.
- colinbeveridge 4y agoNice. I like ln(3) and ln(5) (1.1 and 1.6) as well.
- cperciva 4y agoYeah, ln(3) is useful, although you can also get it from ln(1+x) ~ x. I don't bother remembering ln(5) though; it's just ln(10) - ln(2) anyway.