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View Full Version : how do you find the n'th digit in a quotient of division


paul0n0n
08-30-2009, 08:13 PM
How do you do it?
Here is an example of what I mean.
q = "0.2893798172383982716"
other then doing long division how do you find, say, 7 in q. Or rather is there a formula for finding, if n = 5 the outcome would then be 3 in q. or if n = 13 the outcome would be 8.

why would i want to do this? just cause, i guess, asking and looking at things.

Reedbeta
08-30-2009, 10:41 PM
Well, you know how to do long division, don't you? Just start dividing and keep going until you get to the desired digit.

alphadog
08-31-2009, 12:20 PM
Depends on how far in you want to go. Reedbeta's idea is KISS for low n's. But, if you want mathematical formula (cuz it's getz the chicks, right? Right!?!) a fancy way to get it is that the nth digit of a/b is the 1st digit of (10^(n-1)a mod b)/b, a.k.a. floor(10 * (10^(n-1)a mod b) / b) mod 10.

paul0n0n
08-31-2009, 07:32 PM
That is what I was looking for. And yes it gets chicks!

poita
09-07-2009, 04:20 AM
Convert to a string and then just index it :)

I can't imagine any situation where this would actually be a performance bottleneck.