Name wrote:I generally use the E-15 values for both because usually it's E-15 in the tests I've taken, and the eletron is not 10x denser because it's mass is around 1000x less. Discrepancies like this is basically what makes Fermi annoying. Like for licks to reach center of lollipop I've seen both 2 and 3 for the answers. For questions like ml of blood in a human, the estimate is 4.5-5.5 liters and you lose 2 points even though your answer is technically correctmcmn1619 wrote: I think the idea is to rely on series of estimates of things you do know to estimate the things you don't know.
For this specific question, I have a much better idea of the number of households in the US, the proportions of households with cats, and maybe a less general sense of the proportion of households who currently have cats that are stray.
Also, what are people doing for questions that involve electron/proton radius? Values for this range from the femtometer (e-15) to sub-attometer (e-18 to e-19) lengths; is it just convention to use the classical electron radius (e-15)? If so, then if a proton radius is roughly defined at e-15 as well (which is also debated), then is an electron really over 10X denser than a proton?
While that method of estimating usually works, generally it's kinda off. (Like 1/3 families own cats so 3E7 families that own cats, and with that estimate 3E6 strays while the actual answer is 6E7 cats).
Yeah, I’ve always taken tests with almost all e-15.