There are some approximations that make it easier to do quick mental calculations. Some of the ones I use most are;
(1) Number of seconds in a year = pi x10^7.

(2) speed of light = 1g (9.8m/sec/sec) for one year

(3) 6% for 60 days = 1%

Does anyone out there have any others?

pi = 3.14
e = 2.718
Number of weeks in a year is 52

pi approx = sqrt(10)

speed of light times 1 nano second= 1 foot

1 parsec = pi light years

One of the best fractional approximations to pi is 355/113

355/113=3.14159292035

Pi to 11 places is 3.14159265359

pi = 3.14
e = 2.718
Number of weeks in a year is 52

You're not very smart, are you?

Thanks, ebaines and galacticus. Ebaines, the idea that light moves one foot in 10^-9 sec will be a really useful concept for figuring response times, etc. Rob

You're not very smart, are you?


Oh sorry, you must be one of those people that actually thinks there are 52 weeks in a year.

You asked for useful approximations and I certainly gave you some. In fact the approximations I gave you are much more commonly used than the others I've seen here.

Perhaps my pi approximation is off by the thousandth decimal but it is still the most commonly used approximation.

When I used my slide rule, I entered 22/7 as a close approximation for PI.