Problem solving for a variable in Prime

[factor]

(12-28-2014 10:48 PM)Snorre Wrote:  Hello factor,

I do not know the original problem, but I think the lower limit should not be t but something like either 0 or -∞. (On your calc you seem to have set t to 40, which becomes the lower integration limit). Maybe you're not searching for an s but for t as compsystems suggested (if so, don't name your integration variable also t since it's not forbidden but a bit confusing).
Furthermore I doubt the Prime is able to solve that integral. You should paraphrase it in terms of "erf"/"erfc"/"NORMALD_CDF"/"NORMALD_ICDF" functions and set your lower integration limit and u to concrete values before solving numerically.

Thanks for the explanation. I should have explained more on the original question which is from an article I can't seem to find the link now, and the settings go like this: a math teacher was asking a question to his students in which the students are expected to find the std deviation, s, using the equation z=(t-u)/s, where t is a sample value (of something like height or what, i forgot), and u is the mean. It is also given that z = 0.1 which put the sample in the 10% top. So it is like given that A's height is 40, the mean is 38, and A is within 10% top of the height... the students are expected to do the math to find s.

However, some students unexpectedly devised other creative methods to the problem, and one being using the (other brand calculator's) CAS capability to directly solve the equation (thus from 40 to infinity).

As far as I remember, that equation as typed by that student, although seems very legitimate, didn't give any result other than an error from the (other brand calculator). It turns out some "hints" are required for that equation to work. I have that equation in my calc and wondered if the Prime will solve it faster. And it is faster, compared to the equivalent PC software of that (other brand calculator).