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# Anyone good with statistics ? help needed Watch

1. Hi,

Can someone confirm i have done the right thing and just check my answer ?

My question was what percentage of animals should be between 15cm and 20.5cm in length? (normal distribution) using cummulative normal probability table

mean = 18cm sd= 2cm

using the formula i calculated the z value of 15cm to be -1.5 and z value of 20.5cm to be 1.25. Then I looked up in the table to find the p values, which are :

z=-1.5 (p 0.06681)
z=1.25 (p 0.89435)

and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.

Now i m not sure if this is correct or not, anyone done statistics here ? please look at this and let me know as i dont want to do the wrong thing in my test
2. (Original post by Gamewizard)
and then my conclusion: 0.06% of animals should be between 15cm and 0.89% of animals should be between 20.5.

Now i m not sure if this is correct or not, anyone done statistics here ? please look at this and let me know as i dont want to do the wrong thing in my test
What?! Read your own conclusion - it makes no sense!! "Between 15"? Between 15 and what?

What you actually know from your calculation is:
6.681% of animals should be less than 15cm long
89.435% of animals should be less than 20.5cm long

So you can conclude (and sketching the graph for this to visualise it might help) that:
89.435% - 6.681% = 82.754% of animals should be between 15cm and 20.5cm long
3. (Original post by tomthecool)
What?! Read your own conclusion - it makes no sense!! "Between 15"? Between 15 and what?

What you actually know from your calculation is:
6.681% of animals should be less than 15cm long
89.435% of animals should be less than 20.5cm long

So you can conclude (and sketching the graph for this to visualise it might help) that:
89.435% - 6.681% = 82.754% of animals should be between 15cm and 20.5cm long
Oh right sorry yes read it again, it didnt make sense. Ah damn so my answer was wrong then.

Thank you

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