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March 6, 2009

mean median


just a curious question, for the mean median and mode to be equal among various distributions, must all the terms be identical?
Posted by      Melanie H. at 11:15 AM CST
  Dr. Rebecca Guy  says:
That's one way for these 3 values to be identical.

The mean, median, and mode will also be identical if a distribution is perfectly symmetrical.
Posted on Fri, 6 Mar 2009 11:26 AM CST by Rebecca G.

March 5, 2009

asgn 5


true false 1-3 i feel it would be false because i thought you can not decide causation, is this always the case
1-4 i think it would be true, but i do not really understand the statement
Posted by      Melanie H. at 10:01 PM CST
  Dr. Rebecca Guy  says:
1-3 is false for the reason you state.

1-4 is true as changing the unit does Not change the correlation coefficient

For example, if you had X's and Y's representing dollars and you converted the X's and Y's to cents, the correlation would remain the same.
Posted on Fri, 6 Mar 2009 3:23 AM CST by Rebecca G.

Calculators


i am trying to familiarize myself with all the calculators, when you use the dependent t
calculator, what does p mean and is the t value they give you the t obtained?
Posted by      Melanie H. at 3:43 PM CST
  Dr. Rebecca Guy  says:
The t value given is the calculated value of t or 't obtained.'

The p value is the exact probability of getting 't obtained' (in absolute value .. i.e. no sign) of this size of larger.

In other words, p represents the area to the right of + t obtained and to the left of - t obtained (remember 2 tails).

Hence, if this p value is equal to or less than α, you will ALWAYS reject the null hypothesis.

If this p value is greater than α, you will ALWAYS fail to reject the null hypothesis.
Posted on Thu, 5 Mar 2009 3:47 PM CST by Rebecca G.
  Dr. Rebecca Guy  says:
In other words, you can compare 'p' to 'α' to make your decision instead of using a t critical value.
Posted on Thu, 5 Mar 2009 3:48 PM CST by Rebecca G.

Confidence intervals


with confidence intervals you use the population standard deviation correct?
and i am with justin on his comments. I was worried about talking an online class
and my experience was amazing, your interest and concern as well as quickness to respond meant much to me. For often times in the classroom you do not find that
EveryOnE HaVe A GrEaT BrEaK!
good luck
Posted by      Melanie H. at 3:16 PM CST
  Dr. Rebecca Guy  says:
You use the population standard deviation if it is know. If it is NOT know, substitute the sample standard deviation.

However, once you substitute the sample standard deviation, you must use a critical t instead of a critical z.

Thanks so much for the kind words. :)
Posted on Thu, 5 Mar 2009 3:30 PM CST by Rebecca G.

sorry but this probability i still don't get


What is the probability of drawing four successive cards from a deck of 52 cards and all four cares are aces?
Posted by      Amy G. at 1:20 PM CST
  Dr. Rebecca Guy  says:
With replacement:

The p of 1 ace is 4/52 or 1/13

The probability of an ace followed by an ace followed by an ace followed by an ace equals:

1/13 X 1/13 X 1/13 X 1/13

Don't spend too much time on 'basic probability' -- that is Unit 6. If you will note, I did not devote much time to it in the homework.

There are 0 questions on the final on Basic Probability.
Posted on Thu, 5 Mar 2009 1:45 PM CST by Rebecca G.
  Amy Gaskins  says:
omg. I've spend all day on this.
Posted on Thu, 5 Mar 2009 1:52 PM CST by Amy G.

z score and probability


Can you please explain the concept of z scores and probability. Here is sample question.
The probability of selecting a term from a normal distribution with a z score equal to or less than -2.00 is _____.
Posted by      Amy G. at 12:35 PM CST
  Dr. Rebecca Guy  says:
The normal distribution is a PROBABILITY distribution.

Hence, when you read area, you interpret it as a PROBABILITY.

For example, the probability of selecting a term for a normal distribution with a z score equal to or less than -2.00 is?

Simply read the area BELOW or TO THE LEFT OF -2.00. This area IS the probability.

Nothing more needs to be done since we are conceptualizing the normal distribution as a PROBABILITY distribution.
Posted on Thu, 5 Mar 2009 12:39 PM CST by Rebecca G.

UNIT 6


The probability is .3 that the mean of a sample of 36 terms from an infinite distribution (u=55 and sd=40) will excded what number?
Posted by      Amy G. at 12:23 PM CST
  Dr. Rebecca Guy  says:
First, you will need to find the z score that creates a boundary placing .3 area ABOVE the boundary and .7 area below the boundary.

I did this using the percentile rank calculator. Enter the % of area below this boundary which is .7 times 100 or 70. That is enter 70. The calculator returns a z score of .52.

Now we are working with the one sample z formula:

Here's our substitution:

.52 = (X - 55)/(40/sqrt(36))

.52 = (X - 55)/(40/6) or (X - 55)/6.67

.52 = (X - 55)/6.67

Now solve for X:

X = 58.5

Will exceed what number? 58.5
Posted on Thu, 5 Mar 2009 12:37 PM CST by Rebecca G.

Help with this probability stuff!


Example: What is the probability of orlling an odd number followed by an even number using one balanced die?
Posted by      Amy G. at 11:58 AM CST
  Dr. Rebecca Guy  says:
Sorry.. Redoing.. For some reason I thought you were talking about 1 die initially.

p of odd = 1/2

p of even = 1/2

p of odd follows by an even is 1/2 X 1/2 or 1/4
Posted on Thu, 5 Mar 2009 12:03 PM CST by Rebecca G.
  Dr. Rebecca Guy  says:
On second read.. you are talking about one balanced die.

Answer stands.

p of odd = 3/6 or 1/2

p of even = 3/6 or 1/2

p of odd followed by even = 1/2 X 1/2 or 1/4
Posted on Thu, 5 Mar 2009 12:07 PM CST by Rebecca G.
  Amy Gaskins  says:
I think what's throwing me is the "followed by" leads me to permutation formula.
Posted on Thu, 5 Mar 2009 12:27 PM CST by Amy G.




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