## anonymous 5 years ago The accompanying table shows the scores on a classroom test. What is the population standard deviation x: 100, 95, 90, 80, 75, 72, 70 f: 7, 2, 10, 4, 2, 3, 4

1. anonymous

ooh statistics.....dont remember this but tiere's a formula for Standard Deviation...google it lol

2. anonymous

f stands for frequency, so that's the number of x' of that particular value that occurred. So x = 100 occurred 7 times in the population. x = 95 occurred twice. And so on. Find the mean of your population is the first step. That means summing over all the scores of the class and dividing by the class size.

3. anonymous

$\sum_{n=1}^{3}i^(n-1)$

4. anonymous

5. anonymous

what's that?

6. anonymous

sum?

7. anonymous

What is that sum for formula for?

8. anonymous

the top part means you do the formula on the right 3 times using n=1 n=2 n=3 and then add up all those values

9. anonymous

but the i is raised to the n-1

10. anonymous

What's the formula represent? Is this a different problem? I thought you were asking about standard deviation.

11. anonymous

yeah its a different problem i figured out the other one ill use my calculator

12. anonymous

So what's the sum asking you to do? You want to find an explicit formula for the sum?

13. anonymous

no you need to find the sum of all those terms

14. anonymous

I have a feeling you wrote the problem wrong. As it is, it makes no sense. Unless the teacher just wants you to write: i^(0) + i^(1) + i^(2). That's the sum.

15. anonymous

yeah u do i^1+i^2+i^3 and add them up

16. anonymous

17. anonymous

You raise it to (n-1). So when n = 1, n-1 is 0. So the first power is 0. The next power increased by 1, so it's 1.

18. anonymous

nev ermind its fine..can you look at my probability question

19. anonymous

no i gotta go

20. anonymous

if you post it on here, someone will be sure to help. there's a lot of people on right now

21. anonymous

okk

22. anonymous

good luck