HELP!! Probability...
- Thread starter mrose
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How do you determine the probability of p(x>108) with the standard deviation of 8, and the mean of 100?
I am so lost, I have never been good at math
...and just stop saying or thinking that last part.
Thanks, once someone sat me down and explained it, I got it.. And then once the teacher gave me the table we are suppose to reference to, it all made sense!
I have another question though...
p(84<x<116)
So the Z scores are -2, and 2.... so its 2... When you go to the table which column for the answer do you use? The proportion in the body, because that is where it lies, or do you use the proportion between the mean and z?
I have another question though...
p(84<x<116)
So the Z scores are -2, and 2.... so its 2... When you go to the table which column for the answer do you use? The proportion in the body, because that is where it lies, or do you use the proportion between the mean and z?
- Joined
- Apr 12, 2005
- Messages
- 11,339
Yes, the actual table will help.
You must look at your table and see exactly what it is telling you. There should be a picture with it. This picture will include a shaded region of some sort.
The shaded region may extend all the way to the left tail. This mean your Z-score provides probability from zero. A Z-score of zero will be 1/2. A Z-score of 1 will be (50% left of the mean) + (34ish% right of the mean) for a total of 84%.
Read your chart carefully and make sure you know what it means.
Your task for -2 < Z < 2 is two pieces. Using the style I hinted at above:
1) For Z = 2, the probability left of Z = 2 is 0.977
2) For Z = -2, the probability left of Z = -2 is 0.023
3) Thinking about those shaded regions, notice how #1 INCLUDES #2. Subtract for the aread BETWEEN them. 0.977 - 0.023 = 0.954
4) For future reference, if you want the area Z < -2 or Z > 2 (the outside portions), subtract again: 1 - 0.954 = 0.046, or you could have used symmetry from Z = -2 and calculated it by 2*0.023 = 0.046
You must look at your table and see exactly what it is telling you. There should be a picture with it. This picture will include a shaded region of some sort.
The shaded region may extend all the way to the left tail. This mean your Z-score provides probability from zero. A Z-score of zero will be 1/2. A Z-score of 1 will be (50% left of the mean) + (34ish% right of the mean) for a total of 84%.
Read your chart carefully and make sure you know what it means.
Your task for -2 < Z < 2 is two pieces. Using the style I hinted at above:
1) For Z = 2, the probability left of Z = 2 is 0.977
2) For Z = -2, the probability left of Z = -2 is 0.023
3) Thinking about those shaded regions, notice how #1 INCLUDES #2. Subtract for the aread BETWEEN them. 0.977 - 0.023 = 0.954
4) For future reference, if you want the area Z < -2 or Z > 2 (the outside portions), subtract again: 1 - 0.954 = 0.046, or you could have used symmetry from Z = -2 and calculated it by 2*0.023 = 0.046
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