Summarizing a set of expressions on a TI-83 Plus

April 29, 2006 6:44 AM

How do I easily summarize a set of expressions on my Texas TI-83 Plus calculator?

Say I want to find the probability of something and I have the expression:

(30 nCr X)*(0.9^X)*0.1^(30-X)

Say X goes from 20 to 30, and I want to sum up all the values given by the expression. What is the quickest way to do this?

posted by cheerleaders_to_your_funeral to technology (8 comments total)

It's been awhile since I've used a TI-83, but it ought to be pretty trivial to write a program to do that. I used to write programs on it all the time. It's like BASIC, as I recall, and the manual explains it pretty well.
posted by ludwig_van at 7:33 AM on April 29, 2006

0->y
For(x,20,30)
f(x)+y=y
end
print y

or something like it should be the right thing to make a little loop as a calculator program that'll sum up all those f(x)'s.
http://www.ticalc.org/programming/columns/83plus-bas/cherny/
posted by apathy0o0 at 8:21 AM on April 29, 2006

there is a sum function
it looks like a sideways M
iirc, the syntax is:

Sum(expr, var, lower, upper)
posted by lpctstr; at 11:49 AM on April 29, 2006

I've been using my TI-83 (original) for years, ever since I bought it for high school math. I'm always amazed at how good it is with complex expressions, assuming you're familiar with its features.

I'm not sure if X is supposed to be an integer, but if that's the case, the expression would be:

sum(seq((30 nCr X)*(0.9^X)*0.1^(30-X),X,20,30,1))

"sum" is located in the math submenu of the list button and seq is located in the ops submenu of same.
posted by zixyer at 2:15 PM on April 29, 2006

Oh yeah, and in case you can't figure it out from the example, the syntax of "seq" is seq(exp, var, first, last, delta) which generates a list, each element determined by evaluating exp with var set from first to last incremented by delta. "sum" just gives you the sum of all the elements in a list.
posted by zixyer at 2:27 PM on April 29, 2006

when i need to do things like this i usually enter the expression in the graphing feature. Then look at the table feature to get the values. You can go to 'tableset' and give it a range of values to work with.
posted by I_am_jesus at 6:20 PM on April 29, 2006

zixyer, you got it! Great.

lpctstr;, I think that's actually how it's done on the casio calcs. That's actually why I wanted to know this, that I saw someone do that with their casio.

So yes, thank you my all, I'll now be mister super efficient on my math exam. Woot and yay!
posted by cheerleaders_to_your_funeral at 1:46 AM on April 30, 2006

cheerleaders_to_your_funeral: I think you're right. I may be thinking of the ti89
posted by lpctstr; at 1:53 PM on April 30, 2006