Covariance between Index A and B calculator, between, numbers, please, points

wildrose

A:
-6.4
6.6
12.9
3.2

B:
-6.2
19
-7.7
4


It asks for the covariance...I plugged the numbers into their respective data points in my calculator and got 10.37...wrong answer. Correct answer was 13.82

The explanation says, when done out by hand, you would use n-1 in the denominator when dividing the summation of all the covariances...i thought this was only done for samples?

Help please, thanks.

Bulla564

harley...your numbers must be off somewhere. i did it on EXCEL just now for you to see. i'll send it over if you want it.

e-mail me at: HARVEY.CHAN214 @ GMAIL *DOT* COM



Edited 1 time(s). Last edit at Friday, June 5, 2009 at 01:24PM by JaRvEy.

ogoluwa

If I don't know how to do stuff like this, and std dev, and variance, etc. in my calculator, is it conceivable to learn how to do it in the next hour or two? Is it worth it?

ajpheif16

I did it and got r=.13945, Sx = 8.05, Sy = 12.302. (I used the sample stdn dev, not the population)

.13945 = x/(99.032)

x = 13.81

dcfox83

On the ti

2nd Data (7 key)
enter x and y varianbles
Quit

2nd Stat (8 key) use arrows to find r (correlation) and Sx is sample stnd dev of x, the (standard deviation greek letter) is the population stnd dev.

Saves a lot of time. easy to learn.

thisisbrianly

billy22g Wrote:
-------------------------------------------------------
> If I don't know how to do stuff like this, and std
> dev, and variance, etc. in my calculator, is it
> conceivable to learn how to do it in the next hour
> or two? Is it worth it?


For STD DEV and variance, press 2nd+7 on your TI. enter in your variables as X0, x1, etc. Then press 2nd+8. Scroll down to std dev measurement.

Could someone please post how to do covariance on calculator?

bapswarrior

well thanks to both you and cpk then.

any fast ways to do #115 in the mock exam morning session?

kmf229

you so lost me...
but definitely thanks for the other one cause my head was spinning going back and forth from paper to calculator trying to get it.

sgupta0827

This question was 117# in the mock morning exam. It doesn't have any texts. Does anyone know what would indicate that it should be computed as a sample?

koba

Sorry....for Q 115:

look at the probability part of the question. since they arent all equal, you need to "trick the calculator" becuase the calc thinks every X and Y you enter into the sheet have an equal probability.

To trick the calc, a 20% probability is just two 10% probabilities, so enter the x value 2 times. We'll use 10 total inputs, so 2/10 is 20%.

Same for a 40% probability....just enter the value 4 times.

apply this to the full set and you end up with 10 total x values with probabilities equal to the number of times you used the value...



Edited 2 time(s). Last edit at Friday, June 5, 2009 at 02:17PM by june2009.