## Nickie_S Group Title Statistics The diameters of grapefruits in a certain orchard are normally distributed with a mean of 7.30 inches and a standard deviation of 0.80 inches. Show all work. (A) What percentage of the grapefruits in this orchard have diameters less than 6.7 inches? (B) What percentage of the grapefruits in this orchard are larger than 7.20 inches? What I have wrote out mean=m=7.30 Standard deviation=s=0.80 (A) what % have diameters less than 6.7 (B) what %are larger than 7.20 2 years ago 2 years ago

1. amistre64 Group Title

2. amistre64 Group Title

3. amistre64 Group Title

z = (6.7 - mean)/sd

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6.7-7.30/0.80

5. amistre64 Group Title

good, thats our z score for A

6. amistre64 Group Title

we get a negative and we know that it wants the value of everything to the left of it

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.5 - zvalue

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zvalue will probably be called a Pvalue later in the book

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-0.75

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yep

11. mathTalk Group Title

Can we use the bell curve ?

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we are .

13. Nickie_S Group Title

yes, mathtalk that is what they are all made of (im in statistics-the book says elementary statistics- my first class of it0

14. mathTalk Group Title

somebody show how to proceed here

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16. Nickie_S Group Title

so 0.5000-0.2734(from the table)=

17. amistre64 Group Title

its alot to wrap up form previous posts ... but in a nutshell, you get a zscore and look that up in a table to get a value

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then work it into the question to find an answer

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.2734 is good, so that should do it for A

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B is trickier in that it wants values all to the right of z

21. amistre64 Group Title

same concept, but we have to adjust our thinking a little to accomodate for it

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don't we do 0.5000-0.2734?

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yes

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A is the result of .5 - .2734

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for the first one? right.

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yep

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oh ok, then i have 0.2266

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good

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so then I write it like this right? P(x<6.7)=0.23

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B needs some care taken to it.|dw:1320180861380:dw|

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A asks for a % so we gotta rewrite .2266 as 22.66%

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*100 .2266*100=22.66%

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that looks good to me

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ok, on to the second one!

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are you still here?

36. amistre64 Group Title

im here

37. amistre64 Group Title

lets figure the z score to get started

38. Nickie_S Group Title

ok, I have been having loading problems, so I thought it was me.

39. Nickie_S Group Title

ok

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P(x>7.2)

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wait I am trying to figure it.

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z = (7.2-7.3)/.8 .... same process, different numbers

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x-mean/stan dev. 7.20-7.30/0.80

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-01/0.80 -0.125/0.80 -0.15625

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got some typos in there... but your on the right track -.1/.8 = -.125

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7.2 - 7.3 = -.1 -.1/.8 = -1/8 = -.125

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and then: -0.125/0.80 =-0.15625

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no, there is no need to divide it again by .8

49. Nickie_S Group Title

ok, i see it. ok next step.

50. amistre64 Group Title

$z=\frac{x-\bar x}{\sigma}$ $z=\frac{7.20-7.30}{0.80}$ $z=\frac{-0.10}{0.80}=-0.125$

51. amistre64 Group Title

id go with the z=.13 value, but a better result would be that since this is exactly in between .12 and .13 to take the average of the values as well

52. Nickie_S Group Title

lets go with -0.13

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lets :)

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now I go find it in the table.

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yep, we need the value for this z to calculate with

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0.0517

57. amistre64 Group Title

thats what i got in my table as well

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so do we take 0.5000+0.0517?

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we do, and you understand why right?

60. Nickie_S Group Title

because it is greater, and because it is a positive number

61. amistre64 Group Title

close enough, with more practice it should become better to see it :)

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lol, I'm a begginer.

63. amistre64 Group Title

one way to think of it is to get the value to the left and subtract it from the total value under the curve; the total is 1

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1 - (value to the left of z) = (value to the right of z)

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because the problem is a greater than, so you have to add the left side of the bell with the amount that is greater than the half.

66. amistre64 Group Title

yep, that is a very good way to view it. good job ;)

67. Nickie_S Group Title

well thanks for the medal! (medals).

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and remember its asking for %

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so we get 0.5517

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which makes it a 55.17%

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good

72. Nickie_S Group Title

Ok, I have 2 more questions I need help with, and as I am learning maybe i can do most of the work. So here we go to another question, if your p for it.

73. amistre64 Group Title

im good for it .... :)